X SA I-CHEM - HYDRATED SALT

HYDRATED SALT

→ Water of crystallization is the fixed number of water molecules present in one formula unit of a salt.

→ In coloured crystalline & hydrated salt, the molecules of water of crystallization account for their characteristic colour. Upon heating a hydrated salt, its colour changes since the molecules of water of crystallization are removed & salt becomes anhydrous.

Examples.

(i) CuSO₄. 5 H₂O    →   CuSO₄           +              5H₂O

                (blue)                 (white)

(ii) Gypsum :─ CaSO₄.2H₂O              →                            CaSO₄.1/2H₂O

                                Gypsum                                                 plaster of paris

(iii) Sodium carbonated decahydrate Na₂CO₃.10H₂O

→ Crystalline salts containing molecules of water of crystallization are not wet.

Reason: The molecules of water of crystallization are the part of the crystals. Upon heating there are released, making the salt anhydrous.

PLASTER OF PARIS (CaSO₄.1/2H₂O)

→ It is obtained by heating gypsum at a temperature of 373K in a kiln.

Gypsum :─ CaSO₄.2H₂O                   CaSO₄.1/2H₂O     +              3/2 H₂O

                      Gypsum                           plaster of paris

Temperature must be controlled because at high temperature, plaster of paris gets completely dehydrated to form anhydrous calcium sulphate.

 CaSO₄.2H₂O        →                            CaSO₄ + 1/2H₂O

Calcium sulphate

Or dead burnt plaster

Uses:

It is used

(i)                   for making toys & materials for decoration,

(ii)                 in surgical bandages for setting fractured bones. White powder of plaster of paris, on mixing with water changes to gypsum, giving a hard solid mass.

CaSO₄.1/2H₂O + 3/2H₂O →        CaSO₄.2H₂O                                              

Plaster of paris                                     Gypsum                                

(iii)                for covering the walls & roofs & on making designs on them.

X SAI CHEM - Importance of pH in daily life

Importance of pH in daily life

1. Effect of acid rain

·                     When pH of rain water < 5.6, it is called acid rain. Acid rain flows into the rivers & thus lowers the pH of river water, thus making the survival of aquatic life difficult.

2. Soil pH & plant growth  

·                     Plants require a specific pH range for their healthy growth.

·                     Examples:

Plants	Preferred pH range
Potato	4.5 ─ 6.0
Garlic, Tomato	5.5 ─ 7.5
Onion, Cabbage	6 .0 ─ 7.5

·                     Soil pH can reach as low as 4. The acidic effect can be neutralized by liming the soil by adding Ca(OH)₂, CaCO₃ or CaO.

·                     Soil with excess limestone (alkaline) reaches pH as high as 8.3. So, in order to reduce the alkaline effect, decaying organic matter (acidic in nature) is added.

3.  pH in our digestive system

·                     Our stomach produces dilute hydrochloric acid which helps in the digestion of food. During indigestion the stomach produces too much acid, which causes pain & irritation.

·                     The excessive acids can be neutralized by use of following antacids─

v   Milk of magnesia ─ Mg(OH)₂.

v   Aluminium hydroxide ─ Al(OH)₃

v   Sodium hydrogen carbonate ─ NaHCO₃

4. pH change leads to tooth decay

·                      Tooth decay starts when pH of mouth < 5.5. The hardest substance, tooth enamel (made of calcium phosphate), is corroded when pH < 5.5. Bacteria in mouth produce acids by degradation of sugar & food particles remaining in the mouth after eating. To neutralize excess acid, tooth pastes containing basic ingredients should be used.

5. Self defence by animals & plants through chemical warfare

·                     Stings of bees & ants leaves methanoic acid which causes pain & irritation. Use of a mild base like baking soda on the stung area neutralizes the effect of acid & gives relief.

·                     Effect of stings of wasps containing alkali is neutralized by application of vinegar (ethanoic acid).

·                     Leaves of neetle plant have stinging hair (due to methanoic acid). The effect of acid is neutralized by application of leaves of ‘dock plants’ which grow beside neetle plant.

X- SAII-ACID,BASE & SALT - Q&A

1.      Define an acid?
An acid is a substance which gives H+ ion or hydronium ion , H₃O⁺ in water, (when it disassociate) e.g HCl, H₂SO₄

2.      Define a base.
A base is a substance which gives OH- ion in water , ( when it disassociate) – NaOH, KOH etc.

3.      Name some natural indicators and some synthetic indicators.

Natural indicator: Litmus, turmeric, red cabbage leaves, Petunia, Geranium, Hydrangea etc

Synthetic indicator: Methyl orange, phenolphthalein etc.

4.      What are olfactory indicators?
These are the substances which have different smell (odour) in acidic and basic medium. Olfactory indicators can be used in the laboratory to test whether a solution is a base or an acid, a process called olfactory titration. Onion, clove oil and vanilla extract are examples.

5.      Why does an aqueous solution of an acid conduct electricity?
When an acid is dissolved in water, ions become free to move and hence they can conduct electricity.

6.      What is "water of crystallisation"? 

The fixed number of water molecules present in one formula unit of a crystalline salt is called water of crystallisation, example : CuSO₄.5H₂O 

7.      What is the pH of human blood ? 

Human blood is slightly alkaline with a pH in the range of 7.2 to 7.4. 

8.      What do you understand by dilution of an acid or base? 

Dilution of an acid or base means mixing an acid or base with water to decrease the concentrations of ions (H+ in acids or OH- in bases) per unit volume. 

9.      What is Soda ash ? 

Soda ash is anhydrous sodium carbonate (Anhydrous - Without water molecule. Its formula is Na₂CO₃. 

10.  What are antacids? 

Antacids are weak bases which neutralise the excess acid in the stomach. Example of antacid is milk of magnesia (Mg(OH)₂). .

11.  What is the chemical name of washing soda ? 

The chemical name of washing soda is sodium carbonate decahydrateNa₂CO₃.10H₂O.
Sodium carbonate decahydrate is a hydrated form of soda ash, a common raw material used in numerous industrial processes. Also called washing soda, the compound is used to remove stubborn laundry stains today.

12.  Fresh milk has a pH of 6.How do you think the pH will change as it becomes sour? Explain your answer. 

pH will decrease as the milk becomes sour .It is because sour milk contains lactic acid.

X- SA I-TEST – LIFE PROCESS & LINEAR EQUATION

1.       [1,1]What is peristaltic movement? How helpful are they in human digestion?

2.       [2]Write various the methods used by the plants to get rid of excretory products.

3.       [4]Sketch a flow diagram for the various pathways for breakdown of glucose ( Respiration Flow diagram).   

4.       [5]Draw a well labeled symbolic diagram of human heart showing the passage of flow of blood.

5.       [5]Describe the structure ( labeled diagram)  and functioning of nephron in the human body.

1.       [3]If the numerator and denominator of a fraction are increased by 2 and 1 respectively, it becomes 3/4. If the numerator and denominator are decreased by 2 and 1 respectively, it becomes 1/2. Find the fraction.

2.       [3]Sonali went to a bank to withdraw Rs 2000. She asked the cashier to give her Rs 50 and Rs 100 notes only. Sonali got 25 notes in all. Find how many notes of Rs 50 and Rs 100 she received.

3.       [4]3 men and 4 boys can do a piece of work in 14 days, while 4 men and 6 boys can do it in 10 days. How long would it take 1 boy to finish the work? [ 140 ]

4.       [4]The students of a class are made to stand in (complete) rows. If one student is extra in a row, there would be 2 rows less, and if one student is less in a row, there would be 3 more rows. Find the number of students in the class. [60 ]

5.       [4]A boat goes 30 km upstream and 44 km downstream in 10 hours. In 13 hours, it can go 40 km upstream and 55 km down-stream. Determine the speed of the stream and that of the boat in still water

6.       [HW]A train covered a certain distance at a uniform speed. If the train had been 30 km/hr faster, it would have taken 2 hours less than the scheduled time. If the train were 15 km/hr slower, it would have taken 2 hours more than the scheduled time. Find the length of the journey. [ 360]

7.        [HW]The age of a father is equal to sum of the ages of his 6 children. After 15 years, twice the age          of the father will be the sum of ages of his children. Find the age of the father. [60 ]

8.       [HW]Sheela travels, 300 km to her home partly by train and partly by bus. She takes 4 hours if she travels 60 km by train and the remaining by bus. If she travels 100 km by train and the remaining by bus/ she takes 10 minutes longer. Find the speed of the train and the bus separately.[ 60, 80 ] 

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X CHEM :ACID, BASE & SALT

Q1.            Define (i) Acid (ii) Bases (iii) Salt

 Acid: A substance which turns blue litmus to red sour in taste and liberates hydrogen ions in aqueous solution. Metals react with acids to form salts and liberate hydrogen gas [Most metals don’t react with Nitric Acid to liberate hydrogen as it is highly oxidizing in nature--- Mg and Mn reacts with Nitric Acid to liberate hydrogen] .Many acids are corrosive such as, HNO₃, H₂SO₄, HCl, etc.

Base: A substance that are bitter in taste and change the colour of red litmus to blue .Bases reacts with an acid to form a salt and water only. If dissolved in water, they give hydroxyl ions (OH–) ions.

Salt:  A chemical compound formed when the hydrogen from acid has been replaced by a metal. A salt is also produced  when an acid reacts with a base in neutrilisation reaction. Salts are named according to anion or cation they are formed of.. For example, Sodium salts or Chloride salts .   

Q2.            Why is it advised to clean mouth after consuming food? or

pH change is a cause for toot decay. Explain.

 Acid is produced in the mouth due to the degradation of remains of sugar and food particles after eating, by certain bacteria. As a result the pH of mouth is lowered. Tooth enamel [ made up of calcium phosphate- Hardest substance in our body] gets corroded when the pH in the mouth lowered than 5.5 . So, tooth decay starts when the pH of the decreases below 5.5

Therefore, it is advised to clean the mouth using basic material e.g  toothpastes and mouth wash.

Q3.            How sodium hydroxide is produced? or

What is ‘Chlor-alkali’ process? or

What do we obtain by electrolysis of brine?

 Sodium hydroxide is produced by electrolysis [ passing of electricity] of aqueous solution of sodium chloride (NaCl) [ called Brine ]. Electrolysis of brine results in the decomposition of NaCl and formation of NaOH.

2NaCl (aq) + 2H₂O(liq) → 2NaOH (aq) + Cl₂(g) + H₂(g)

The process is named ‘chlor-alkali’ process because the products formed  - chlor for chlorine and alkali for sodium hydroxide. Chlorine is given off at the anode while hydrogen at cathode.  

Q4.            What is ‘water of crystallization’?

 Water of recrystallization is a fixed number of water molecules present in one formula unit of salt. These are called hydrated salt. For example,

(Na₂CO₃.10H₂O)        → 10 water molecules present as water of crystallization.

CuSO₄.5H₂O               → 5 water molecules present as water of crystallization.

CaSO₄.2H₂O               → 2 water molecules present as water of crystallization.

The water of crystallization remain in chemical combination with crystal. It doesn’t make the crystal wet . It is essential for the maintenance of crystalline properties of the crystal. such as its shape and colour .It can be removed by sufficient heat. By loosing water molecules the crystal looses its colour and shape as well.

Q5.            What are hydrated salts? Give an example.

 Salts containing a fixed number of water molecules in their crystal structure are called hydrated salts.

A molecule of sodium carbonate (Na₂CO­₃.10H₂O) contains ten molecules of water. This is known as hydrated salt of sodium carbonate [ called Washing Soda].

Q6.            Name some chemicals obtained by using sodium chloride (common salt) as a raw material.

Sodium hydroxide (NaOH),

Baking soda (NaHCO₃),

Bleaching powder (CaOCl₂), etc.

Washing soda (Na₂CO­₃.10H₂O),

Q7.            What are strong and weak acids?

 acids that give rise to more H+ ions are said to be strong acids and vice-versa acids. A strong acid has pH value closer to zero while acids with higher pH values or closer to 7 are weak acids.  

Q8.            What is ‘Plaster of Paris’?

Q9.             when gypsum is heated at 3730 K, it loses some of its water molecules and becomes calcium sulphate hemihydrates (CaSO₄.1/2 H₂O). This is called ‘Plaster of Paris’.

CaSO₄.2 H₂O) → CaSO₄.1/2 H₂O + 3/2 H₂O

Q10.        What is Universal Indicator?

 Universal Indicator [ UI ]  is a mixture of several indicators. The universal indicator shows different colours at different concentration of hydrogen ions in a solution. Hence with the help of a UI  we can judge how strong a given acid or base is. 

Q11.        Why do HCl, HNO₃, etc. show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

 HCl and HNO₃ etc. disintegrate in presence of water to form hydrogen ions (H+). Since hydrogen ions can’t exist alone they combine with H₂O to form hydronium ions (H₃O⁺). The reaction can be given as follows:

HCl → H⁺ + Cl^–

H+ + H₂O → H₃O⁺

Because of this property HCl and HNO₃ show acidic character in aqueous solutions. On the other hand, alcohol and glucose can not disintegrate or dissociate in water to form hydrogen ions. Hence, they do not show acidic character. 

Additional Information: Also these (alcohol and glucose) are not capable of conducting electricity as these don’t produces ions which are essential for conduction of electricity. 

Q12.         Why does an aqueous solution of acid conduct electricity?

 When dissolved in water, acids disintegrate to form ions e.g.,

HCl + H₂O → Cl^– + H₃O⁺   

These ions are responsible for electrical conductivity.

Q13.        Why does dry HCl gas not change the colour of the dry litmus paper?

 We know that the colour of the litmus is changed by H⁺ ions of an acid. Dry HCl does not disintegrate to give H⁺ ions. It is only in the aqueous medium that an acid disintegrate to give ions. Since both HCL and litmus paper don’t contain water the colour of litmus paper does not change.