Pracs

Question 1

Outline the method you would use to test a natural indicator that has been prepared in the school laboratory

Answer 1

1. prepare solutions of pH 1,3,5,7,9,11 by starting with 1 mo/LHCl and NaOH and progressively diluting them until these pHs are measured.
2. Set up 6 test tuibes with 5 mk of solution of the different pHs in each.
3. Add 1ml of the red cabbage indicator already prepared to the test tube.
4. Record the colour the indicator turns at each pH

Question 2

How does concentrated H2SO4 work as a dehyrdating agent with crystalline hydrates?

Answer 2

when conc. h2so4 is heated with crystalline hydrates, it frequently dehydrates them.

eg. CuSO4.5H2O(s) —-> CuSO4(s) + 5H2O
copper II sulfate pentahydrate(blue) —-> anyhydrous copper II sulfate (white)

Question 3

How does concentrated H2SO4 work as a dehyrdating agent with compounds that contain hydrogen and oxygen?

Answer 3

C2H5OH –> C2H4 +H2O

Question 4

What is the aim for the prac involving h2so4 as a dehydrating agent?

Answer 4

Aim: to react sucrose with concentrated sulfuric acid

Question 5

What is the method for the prac involving h2so4 as a dehydrating agent?

Answer 5

1. place approx. 2cm of sucrose of sucrose into large test tube in a test tube rack in fume hood.
2. Add 2ml of concentrated sulfuric acid

Question 6

What is the result for the prac involving h2so4 as a dehydrating agent?

Answer 6

the sugar caramlises and turns frombrown to black, as the water is being removed. This results in a column of carbon , the intense heat and water eporation makes the column ‘grow ‘

Question 7

What is the conclusion for the prac involving h2so4 as a dehydrating agent?

Answer 7

h2so4 absorbs water, causing dehydration.

C12H22O11 + 11H2SO4 —> 12C + 11H2SO4.H2O

Question 8

What is the aim for the prac involving h2so4 as n oxidising agent?

Answer 8

Aim: to react dilute h2so4 with samples of magnesium and zinc to compare rate of ocidation at various dilutions

Question 9

What is the method for the prac involving dilute h2so4 as n oxidising agent?

Answer 9

method:

1. add small pieces of Mg, Fe and Zn in separate beakers separatley into 3 beakers
2. Add 3 drops of conc. H2So4 to eeach.
3. observe reaction vby monitor the rate of fizzing from 0-5 (0 being no fizz, 5 being lotsa fizz !!)

Question 10

What is the aim for the prac involvinconc.2so4 as an oxidising agent?

Answer 10

to react conc. h2so4 with a sample of K bromide

Question 11

What is the method for the prac involving dilute h2so4 as n oxidising agent?

Answer 11

in a fumehood add some conc. h2so4 to a sample of potassium bromide in a tst tube.
repeat with dilute h2so4

Question 12

What are the results for the prac involving dilute h2so4 as an oxidising agent?

Answer 12

with conc. acid, the mixture darkens as the bromine ion is oxidised to bromine
Br2+ —> Br(s)

Question 13

method for modelling equilibrium?

Answer 13

• we used a plastic bole of water suspended above a tank of water
• the plastic bottle had a stoppered hole in it so that the water flowed from it into the tank,
• water from the tank was fed back into the top of the bottle by tubing connected to a small water pump
• we turned the pump on and took the stopper out of the bottle to model the equilibrium reaction
• to model the effect of increase in the concentration of reactant , we added water to the bottle
• to model effect of a catalyst, we increased the speed of the pump.

Question 14

what is the validity for modelling equilibrium ?

Answer 14

• method is valid as it was a qualitative model of an equilibrium reaction eg. it shows that the process occurs in 2 directions
• it also oberved that the over all level of water in the tank is constant
• the characteristic of the constant microscopic change of equilibrium system is also observed, with water continuously flowing into and out of the tank.