Acids, Bases and Salts
Competition questions
25 marksCalcium oxide and magnesium sulfide each react with acid.
CaO(s) + 2H+(aq) → Ca2+(aq) + H2O(l)
MgS(s) + 2H+(aq) → Mg2+(aq) + H2S(g)
A mixture of these two compounds, X, reacts with exactly 0.125 mol of dilute hydrochloric acid. The amount of hydrogen sulfide formed is 0.0250 mol. What is the mass of calcium oxide in mixture X?
2024 CHS O Prelim P1 Q12
The mineral dolomite is a double carbonate of magnesium and calcium, CaMg(CO3)2. When 2.00 g of an impure sample of dolomite was completely dissolved in excess hydrochloric acid, 0.45 g of carbon dioxide was given off. CaMg(CO3)2 + 4HCl → MgCl2 + CaCl2 + 2CO2 + 2H2O. What is the percentage purity of the sample?
2024 SNGS O Prelim P1 Q11
Excess magnesium powder is added to 25 cm3 of 0.10 mol/dm3 solutions of three different acids: (1) methanoic acid, HCOOH, a weak monobasic acid, (2) hydrochloric acid and (3) sulfuric acid. Which statement is correct?
2023 SJI O Prelim P1 Q19
The table shows the results of experiments on two acids, K and L, of equal concentration.
| K | L | |
|---|---|---|
| conductance / mS | 400 | 7.0 |
| temperature change when excess acid reacted with 200 cm3 of 1.00 mol/dm3 sodium hydroxide / °C | 6.9 | 6.7 |
| reaction with magnesium | rapid effervescence | gradual effervescence |
Which deduction can be made about the two acids?
2024 Bukit View O Prelim P1 Q21
All ammonium salts produce ammonia gas when heated with sodium hydroxide. From which ammonium salt can the greatest mass of ammonia be obtained?
2024 Zhonghua O Prelim P1 Q31
A sodium nitrate solution is prepared by adding 0.10 mol of sodium nitrate, NaNO3, to 2.00 L of water. Which of the following is incorrect?
2023 SJChO P1 Q9
Which of the following has the lowest pH?
2023 SJChO P1 Q10
Rainfall from unpolluted air should be
2023 SJChO P1 Q41
To obtain the magnesium compound in a mineral ore containing impurities of Al2O3 and P4O10, which reagent could be used to dissolve the impurities in the ore?
2024 CJC J2 Prelim P1 Q6
Which pair is not a Brønsted–Lowry conjugate acid–base pair?
SJChO Mock 3 P1 Q6
Which statement about the ammonium ion, NH4+, is incorrect?
2018 NYJC J2 MYE P1-P3 Q3
In which reactions does NH3 behave as a Lewis base?
1 2NH3 → NH2− + NH4+
2 HSO4− + NH3 → SO42− + NH4+
3 Ag+ + 2NH3 → [Ag(NH3)2]+
2019 NJC J2 Prelim P1 Q12
The following reaction takes place in a suitable solvent: Na+NH2− + NH4+Cl− → Na+Cl− + 2NH3. Which statements explain why this is a Brønsted–Lowry acid–base reaction?
1 NH2− is an electron pair acceptor.
2 NH2− and NH3 are a conjugate acid–base pair.
3 The ammonium ion acts as a proton donor.
2021 TMJC J2 Prelim P1 Q13
BF3 reacts with (CH3)3N to give (CH3)3NBF3. Which statement is correct?
2023 NYJC J2 Prelim P1 Q4
Ammonium carbonate is a crystalline solid. On gentle warming a reaction occurs, forming ammonia as one product. How are the carbonate ions behaving during this reaction?
2024 NJC J2 Prelim P1 Q9
A sample of solid magnesium hydroxide is prepared by adding an excess of aqueous sodium hydroxide to an aqueous solution containing 1.20 g of magnesium sulfate. The mass of magnesium hydroxide collected is 0.32 g. What is the percentage yield?
2024 PLMGSS O Prelim P1 Q20
10.0 cm3 of 0.10 mol/dm3 lead(II) nitrate, Pb(NO3)2, is added to 30.0 cm3 of 0.05 mol/dm3 sodium chloride, NaCl. After the reaction a white precipitate of lead(II) chloride is present. What else is present?
2024 Serangoon O Prelim P1 Q20
Leo accidentally contaminated a sample of pure lead(II) sulfate with a small amount of lead(II) carbonate. Which sequence of steps would help Leo re-obtain pure lead(II) sulfate?
Source: 2023 SJI O Prelim P1 Q2
20 cm3 of an aqueous 1.0 mol/dm3 solution of the hydroxide of metal X exactly neutralises 40 cm3 of 0.25 mol/dm3 dilute sulfuric acid. What is the formula of the sulfate of X?
2024 Dunman O Prelim P1 Q13
A sample of lithium oxide, Li2O, is dissolved in 250 cm3 of distilled water. 25.0 cm3 of the solution is neutralised by 30.0 cm3 of 0.5 mol/dm3 dilute sulfuric acid. What is the mass of lithium oxide dissolved in the 250 cm3 of water?
2024 AES O Prelim P1 Q16
Dilute sulfuric acid, dilute nitric acid and dilute ethanoic acid were separately titrated with 0.10 mol/dm3 aqueous sodium hydroxide. The same volume and concentration of each acid was used. In order to react completely,
2024 SNGS O Prelim P1 Q12
A tablet of aspirin, C9H8O4, is crushed and dissolved in water. The acid in the tablet is neutralised by 12.25 cm3 of 0.147 mol/dm3 sodium hydroxide: C9H8O4 + NaOH → C9H7O4Na + H2O. One grain of aspirin is 0.0648 g. How many grains of aspirin are there in the tablet? [Mr: C9H8O4 180]
2024 BTYSS FYE O EOY P1 Q12
Oxalic acid, H2C2O4, is a dibasic acid. 25.0 cm3 of oxalic acid solution reacts completely with 15.0 cm3 of 2.50 mol/dm3 aqueous sodium hydroxide. What is the concentration of the oxalic acid?
2024 QTSS O Prelim P1 Q11
Group 1 and Group 2 ionic hydrides react with water: H− + H2O → OH− + H2. In an experiment, 1.01 g of a sample of an ionic hydride is dissolved in excess water. The resulting solution required 24.0 cm3 of 2.0 mol dm−3 HCl for complete neutralisation. What is the formula of the hydride?
2023 ACJC J2 Prelim P1 Q6
The salt (C2H5)4N+Cl− is reacted with hydrogen chloride to form a white solid X, which is dissolved in water to form an acidic solution. 20 cm3 of this solution required 24.6 cm3 of 0.1 M NaOH for neutralisation. Another 20 cm3 of the same solution needed exactly 49.2 cm3 of 0.1 M aqueous AgNO3 for complete precipitation of AgCl. What is the anion in solid X?
2023 SJChO P1 Q2
