Table 1 shows observations from an analysis of a clear solution used to regenerate an ion-exchange water softener. Fig. 1 shows the flame test carried out o...
Question 1 Report
Table 1 shows observations from an analysis of a clear solution used to regenerate an ion-exchange water softener. Fig. 1 shows the flame test carried out on the dried solution.
| test | observation |
|---|---|
| flame test | yellow flame |
| acidified silver nitrate | white precipitate |
| add sodium hydroxide | no precipitate |
(a) Name the positive ion identified by the flame test. [1]
(b) Name the negative ion identified by the silver nitrate test. [1]
(c) Give the formula of the compound in the solution. [1]
(d) Suggest why no precipitate forms with sodium hydroxide. [1]
(e) Use Table 1 to state the colour of the silver chloride precipitate. [1]
A quality controller checks a liquid fertilizer before it is pumped into tanks. Fig. 1 shows two test tubes. Tube A contains the fertilizer with sodium hydroxide and is warmed. Tube B contains a known ammonium chloride solution tested in the same way.
Both tubes produce a gas that turns damp red litmus paper blue.
(a) Name the ion in tube A. [1]
(b) Give the reagent added to both tubes. [1]
(c) Suggest why tube B is included. [1]
(d) Complete the statement: the blue litmus result shows that the gas is ______. [1]
(e) Give one reason why the sample should not be heated in a sealed test tube. [1]
Answer Details
Water-softener regenerating solution
- (a) A yellow flame identifies sodium ions, \(\text{Na}^+\). [1]
- (b) Acidified silver nitrate giving a white precipitate identifies chloride ions, \(\text{Cl}^-\). [1]
- (c) The compound is \(\text{NaCl}\). [1]
- (d) No precipitate forms with sodium hydroxide because sodium hydroxide is soluble; sodium ions do not form an insoluble hydroxide. [1]
- (e) The silver chloride precipitate is white. [1]
Fertilizer test
- (a) Tube A contains ammonium ions, \(\text{NH}_4^+\). [1]
- (b) The reagent added is sodium hydroxide solution. [1]
- (c) Tube B is a positive control: it confirms that the method and reagents are working correctly. [1]
- (d) A gas that turns damp red litmus blue is alkaline. [1]
- (e) A sealed test tube must not be heated because gas pressure could build up and force out the stopper or break the apparatus. [1]
Download The App On Google Playstore
Everything you need to excel in your exams
