Form 4 Chapter 7 (Activity answer)

Activity 12

1	Standard solution – a solution in which its concentration is accurately  known
5	(a)	Calculate the mass of solute needed. Weigh out the exact mass of solute needed in a weighing bottle. Dissolved the solute in a small amount of distilled water.
	(b)	·         Wash and rinse the weighing bottle ,small beaker and filter funnel to ensure  no solute remains in any  of the apparatus used. Transfer the dissolved solute into a suitable volumetric flask.
	(c)	Add more water carefully to the volumetric flask and swirl gently. Shake well to ensure thorough mixing.
	(d)	Add water slowly by using a dropper to bring the level of the solution to the calibration mark. The volumetric flask is closed tightly and inverted several times to get a uniform or homogenous solution.

Activity 13:

3	(a)	Calculate the volume of stock solution required.
	(b)	Use a pipette to draw up the required volume of stock solution.
	(c)	Transfer the stock solution to a suitable volumetric flask.
	(d)	Add water slowly by using a dropper to bring the level of the solution to the calibration mark. The volumetric flask is closed tightly and inverted several times to get a uniform or homogenous solution.

Activity 14:

1 2 3 4

(a) hydrogen dissociation/ionization         b) concentration        (c) concentration, alkali Higher, hydrogen Higher, hydroxide Decrease, increase

Activity 15

3	(a) 2HNO3   +           Ba(OH)2 (aq)             →          Ba(NO3)2 (aq)      +   H2O  (aq)
	(b)  H2SO4   +        2NaOH (aq)             →          Na2SO4 (aq)      +  2H2O  (aq)
	(c)  2H3PO4   +        3Ca(OH)2 (aq)          →        Ca3(PO4)2 (aq)      +  6H2O  (aq)
	(d)  CH3COOH   +        KOH (aq)           →          CH3COOK (aq)      +  H2O  (aq)

Activity 16

3	Indicator Colour in solution of: Acid Alkali Red litmus paper - blue Blue litmus paper red - Phenolphthalein colourless pink Methyl orange red yellow

Activity 18

1(a)	Initial burette readings: 0.80 cm3, 13.40 cm3, 25.90 cm3 Final burette readings : 13.40 cm3, 25.90 cm3, 38.40 cm3
(b)	Titration No. I II II Initial burette reading/cm3 0.80 13.40 25.90 Final burette reading/cm3 13.40 25.90 38.40 Volume of acid used/cm3 12.60 12.50 12.50
(c)	Volume of acid used = 12.60 + 12.50 + 12.50                                                 3                                    = 12.50 cm3
(d)	2 mol dm-3
(e)	6.25 cm3
(f)	Strong acids: hydrochloric acid, sulphuric acid, nitric acid Weak acids: ethanoic acid, carbonic acid
(g)	Pink to colourless
(h)	Yellow to red
(i)	HCl   +   NaOH         -->     NaCl   +   H2O

Activity 19

1	(a)(i)	Sodium hydroxide/ potassium hydroxide r: formula	1
	(ii)	-->2NaOH  +  H2SO4           Na2SO4   +   2H2O / 2KOH   +  H2SO4   -->        K2SO4   +    2H2O -         Chemical formulae of reactants and products correct -         Equation is balanced	1 1
	(iii)	soap	1
	(iv)	Y	1
	(b)(i)	W / X	1
	(ii)	-         W is added into sodium carbonate/any metal carbonate stated in a test tube, -         Gas released turns lime water cloudy / - magnesium/zinc  is added into W in a test tube, - gas released gives a ‘POP’ sound with a lighted splinter	1 1
	(iii)	-         W is a strong acid and X is a weak -         W completely dissociates in aqueous solution to produce high concentration of hydrogen ions.     / X dissociates partially in aqueous solution to        produce low concentration of hydrogen ions.	1 1