Question

A student performed an experiment similar to the one that you will perform, but using different solutions from the ones that you will use. The student's data are presented in Table 4 below.

1.) Is a 0.1 M solution of NaNO2 acidic or basic?

2.) What experimental evidence supports your answer?

3.) List the solutions studied by the student that are basic.

4.) What experimental evidence supports your answer?

Table 4 Student data for estimating the PH of solutins

   indicator color

0.1 M Solution	methly violet	methyl orange	thymolphthalien	phenolphthalein
NH2OH	violet	yellow	light blue	red
HNO2	violet	red	colorless	colorless
C2H2NH2	violet	yellow	blue	red
NaNO2	violet	yellow	colorless	light pink
Ca(OH)2	violet	yellow	blue	red

5.) Using these data, compare the relative basicity of the Ca(OH)2 and C2H5NH2 solutions. Briefly explain on what basis you can or cannot make this comparison.

6.) List the basic solutions in order of increasing basicity.

7.) What experimental evidence supports your answer?

Answer 1

1) NaNO2 will hydrolyze as

NaNO2 + H2O --> NaOH + HNO2

HNO2 is a weak acid and NaOH is strong base, so the solution will be basic as NaOH is basic and HNO2 is acidic

2) NaNO2 gives pink colour in phenolphthalein (it gives pink colour in strong basic medium) so the solution should be strongly basic

3) The solutions which are basic

a) NH2OH

b) C2H2NH2

c) NaNO2

d) Ca(OH)2

4) There is no change in colour of methyl orange in the above three basic solutions. so the solutions are not acidic, must be basic then

5) The relative basicity will be :

WE can not compare the basicity of the two as they both are giving same colour change in all the indicators

6) NH2OH = Ca(OH)2= CH2NH2 > NaNO2 > HNO2

As per the given data

7) the change in colour supports the answer

To give a better idea about the given indicators and given compound

a) Methyl violet : the ph range is 0-2 ( so change in colour for only highly acidic solutions, no solution is highly acidic here hence)

b) Methyl oragne : pH range = 3.1 - 4.4

So above 4.4 the colour will be yellow and below 3.1 the colour red (only acidic solution is HNO2)

c) thymolphthalien : 9.3 - 10.5

Above 10.5 the colour will be blue

so NH2OH will be less basic then C2H2NH2 and Ca(OH)2 however HNO2 and NaNO2 will be less basic then NH2OH

d) phenolphthalein: pH range 8.3 - 10