X CHEMISTRY- ACID,BASE & SALT -Q&A: 2

Q1.            Why do HCl, HNO3, etc. show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

Ans: 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. 

Q2.             Why does an aqueous solution of acid conduct electricity?

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

HCl + H₂O → Cl^– + H₃O⁺   

These ions are responsible for electrical conductivity.

Q3.            Why does dry HCl gas not change the colour of the dry litmus paper?

Ans: 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.    

X CHEMISTRY-ACID,BASE & SALTS: Q & A

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

Ans: 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Salt:  A chemical compound formed when the hydrogen from acid has been replaced by a metal.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 anon 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.

Ans: 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?

Ans: 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’?

Ans: 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.

Ans: 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.

Ans:

Sodium hydroxide (NaOH),

Baking soda (NaHCO₃),

Bleaching powder (CaOCl₂), etc.

Washing soda (Na₂CO­₃.10H₂O),

Q7.             What are strong and weak acids?

Ans: 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’?

Ans: 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

Q9.             What is Universal Indicator?

Ans: 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. 

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X MATHS POLYNOMIAL QUESTIONS SA I[2]

1.     On dividing the polynomial 3y³ – 4y² – 3y + 25 by a polynomial g(y), the quotient and remainder  were 3y + 5 and 5 respectively, find g (y).                                                                                                                                                                       

2.      The area of a rectangle remain the same if its length is increased by 7 cm and the breadth is decreased by 3 cm. The area remains unaffected if length is decreased by 7 cm and the breadth is increased by 5 cm. Find length and breadth.

3.       A no. consists of three digits whose sum is 17. The middle one exceeds the sum of other two by 1. If the digits are reversed, the no. is diminished by 396. Find the no.

4.     On dividing the polynomial 3x⁴ – 14x³+ 12x² + 6x + 5 by a polynomial g(x), the quotient and remainder were x² – 4x – 1 and 32x + 12 respectively, find g (x).                                                                     

5.       If the polynomial 3x³– 4x² – 17x + k is exactly divisible by 3x – 1 find the value of k..                         

6.       Solve for x and y :    2^x + 3^y = 17  and 2^{x + 2} – 3 ^y+1 = 5.

7.       If the polynomial 6x³+ 16x² + px – 5 is exactly divisible by 3x + 5, find the value of p.                          

8.   What real number should be subtracted from the polynomial 2x³+ 5x² – 14x + 10 so that the polynomial 2x – 3 divides it exactly?                  

9.       Find value of k so that the equations x + 2y = – 7, 2x + ky + 14 = 0 will represent coincident lines.

10.   Divide the polynomial (x⁴ + 1) by (x – 1) and verify the division algorithm.

11.   Find the polynomial of least degree which should be subtracted from the polynomial

x⁴ + 2x³– 4x² + 6x – 3 so that it is exactly divisible by x² – x + 1                                                                                       

12.   Give linear equations which is coincident with 2 x + 3y - 4 = 0 Find the value of K so that the pair of linear equations :          (3 K + 1) x + 3y – 2 = 0 

                                              (K² + 1) x + (k–2)y – 5 = 0 is inconsistent.

13.   Verify that – 2 is a zero of the polynomial 9x³+ 18x² – x – 2. Obtain all the zeroes .

14.   Find all the zeroes of 2x⁴ – 3x³– 3x² + 6x – 2, given that two of its zeroes are √2  and – √2 .  

15.   If two zeroes of the polynomial x⁴ – 6x³– 26x² + 138x – 35 are 2 ±√3  find other zeroes.      

16.   Find all the zeroes of the following polynomials :  (i) x³– 2x² – x + 2      (ii) 2x³  –  x² – 13x – 6.               

17.   If (x – 2) is a factor of x³+ ax² + bx + 16 and a – b = 6 find the values of a and b.       

        Ans:

1	[y2 – 3y + 4	6	FYS	11	x – 1	16	[(i) 1,2, -1 ;(ii) 3, -2 , -1/2 ]
2	Find Your self [FYS]	7	7	12	FYS	17	-2 , -8
3	FYS	8	7	13	[– 2 , 1/3 – 1/3
4	Q = 3x2 – 2x + 7	9	FYS	14	1, 1/2
5	6	10		15	7, -5

X MATHS POLYNOMIAL QUESTIONS SA I[1]

                                                                            

1.     On dividing the polynomial 3y³ – 4y² – 3y + 25 by a polynomial g(y), the quotient and remainder were 3y + 5 and 5 respectively, find g (y).                                                                                                                                                                        

2.     The area of a rectangle remain the same if its length is increased by 7 cm and the breadth is decreased by 3 cm. The area remains unaffected if length is decreased by 7 cm and the breadth is increased by 5 cm. Find length and breadth.

3.       A no. consists of three digits whose sum is 17. The middle one exceeds the sum of other two by 1. If the digits are reversed, the no. is diminished by 396. Find the no.

4.     On dividing the polynomial 3x⁴ – 14x³+ 12x² + 6x + 5 by a polynomial g(x), the quotient and remainder were x² – 4x – 1 and 32x + 12 respectively, find g (x).                                                                     

5.       If the polynomial 3x³– 4x² – 17x + k is exactly divisible by 3x – 1 find the value of k..                         

6.       Solve for x and y : 

2^x + 3^y = 17

2^{x + 2} – 3 ^y+1 = 5.

7.       If the polynomial 6x³+ 16x² + px – 5 is exactly divisible by 3x + 5, find the value of p.                          

8.   What real number should be subtracted from the polynomial 2x³+ 5x² – 14x + 10 so that the polynomial 2x – 3 divides it exactly?                  

9.       Find the value of k so that the equations x + 2y = – 7, 2x + ky + 14 = 0 will represent coincident lines.

10.   Divide the polynomial (x⁴ + 1) by (x – 1) and verify the division algorithm.

11.   Find the polynomial of least degree which should be subtracted from the polynomial

x⁴ + 2x³– 4x² + 6x – 3 so that it is exactly divisible by x² – x + 1                                                                                       

12.  Give linear equations which is coincident with 2 x + 3y - 4 = 0 Find the value of K so that the pair of linear equations :

 (3 K + 1) x + 3y – 2 = 0 

 (K² + 1) x + (k–2)y – 5 = 0 is inconsistent.

13. Verify that – 2 is a zero of the polynomial 9x³+ 18x² – x – 2. Obtain all the zeroes of the given polynomial.                                                                                                                                                                                                                                                                              

14.   Find all the zeroes of 2x⁴ – 3x³– 3x² + 6x – 2, given that two of its zeroes are √2  and – √2 .  

15.   If two zeroes of the polynomial x⁴ – 6x³– 26x² + 138x – 35 are 2 ±√3  find other zeroes.      

16.   Find all the zeroes of the following polynomials :

(i) x³– 2x² – x + 2      (ii) 2x³  –  x² – 13x – 6.                                               

17.   If (x – 2) is a factor of x³+ ax² + bx + 16 and a – b = 6 find the values of a and b.       

        Ans:

1	[y2 – 3y + 4	6	FYS	11	x – 1	16	[(i) 1,2, -1 ;(ii) 3, -2 , -1/2 ]
2	Find Your self [FYS]	7	7	12	FYS	17	-2 , -8
3	FYS	8	7	13	[– 2 , 1/3 – 1/3
4	Q = 3x2 – 2x + 7	9	FYS	14	1, 1/2
5	6	10		15	7, -5