Lab 1236

Question 1

Which reagent is commonly used to detect sulfate (SO₄²⁻) ions?

Answer 1

Barium chloride (BaCl₂)

Barium chloride forms a white precipitate of barium sulfate (BaSO₄) when sulfate ions are present.

Question 2

What happens when hydrochloric acid (HCl) is added to a carbonate (CO₃²⁻)?

Answer 2

Effervescence occurs due to CO₂ gas release

The reaction produces carbon dioxide gas, water, and a salt.

Question 3

Which anion does NOT produce a precipitate with silver nitrate (AgNO₃)?

Answer 3

Nitrate (NO₃⁻)

Nitrate ions remain soluble and do not form a precipitate with silver nitrate.

Question 4

What color precipitate does silver chloride (AgCl) form in a qualitative analysis test?

Answer 4

White

Silver chloride is a white solid that precipitates out in the presence of chloride ions.

Question 5

What is the product when sulfate (SO₄²⁻) reacts with barium chloride (BaCl₂)?

Answer 5

BaSO₄ (insoluble in water)

Barium sulfate is a white precipitate that is insoluble in water.

Question 6

Which of the following anions can be detected using the brown ring test?

Answer 6

Nitrate (NO₃⁻)

The brown ring test is a classic method for detecting nitrate ions in a solution.

Question 7

Why is nitric acid (HNO₃) added before silver nitrate (AgNO₃) in the test for halides?

Answer 7

To provide an acidic medium and remove interfering anions

This step ensures accurate results by preventing false positives from other ions.

Question 8

Which anion reacts with lead(II) nitrate (Pb(NO₃)₂) to form a yellow precipitate?

Answer 8

Iodide (I⁻)

Lead(II) iodide (PbI₂) forms a distinctive yellow precipitate.

Question 9

Which of the following anions forms a white precipitate with barium chloride (BaCl₂) in the presence of hydrochloric acid?

Answer 9

Sulfate (SO₄²⁻)

Barium sulfate precipitates out when sulfate ions are present.

Question 10

What gas is released when carbonates (CO₃²⁻) react with hydrochloric acid (HCl)?

Answer 10

Carbon dioxide (CO₂)

The reaction between carbonates and hydrochloric acid produces CO₂ gas as a byproduct.

Question 11

Which reagent is used to detect chloride (Cl⁻) ions by forming a white precipitate?

Answer 11

Silver nitrate (AgNO₃)

Silver chloride (AgCl) precipitates out when chloride ions are present.

Question 12

What is the balanced chemical equation for the reaction of sodium carbonate (Na₂CO₃) with hydrochloric acid (HCl)?

Answer 12

Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O

This equation shows the complete reaction of sodium carbonate with hydrochloric acid.

Question 13

How can sulfate (SO₄²⁻) and carbonate (CO₃²⁻) ions be distinguished using BaCl₂?

Answer 13

Sulfate forms a white precipitate that does not dissolve in acids, while carbonate dissolves with effervescence

This distinguishing feature helps in identifying the two ions.

Question 14

Which of the following is the confirmatory test for nitrate (NO₃⁻) ions?

Answer 14

Brown ring test

This test specifically confirms the presence of nitrate ions in a sample.

Question 15

Which of the following steps correctly identifies chloride (Cl⁻), sulfate (SO₄²⁻), and nitrate (NO₃⁻) in a sample?

Answer 15

AgNO₃ for Cl⁻, BaCl₂ for SO₄²⁻, and FeSO₄ + H₂SO₄ for NO₃⁻

This sequence of tests is used for the qualitative analysis of these anions.

Question 16

Which of the following statements is true regarding the brown ring test for nitrate (NO₃⁻) ions?

Answer 16

It involves FeSO₄ and concentrated H₂SO₄, forming a brown ring at the interface

This test relies on the reaction between iron(II) sulfate and concentrated sulfuric acid.

Question 17

Why does BaSO₄ remain insoluble in hydrochloric acid (HCl), while BaCO₃ dissolves?

Answer 17

BaCO₃ reacts with HCl to release CO₂ gas, while BaSO₄ is highly insoluble

This difference in solubility is key in distinguishing between these compounds.

Question 19

What is the purpose of adding ammonium hydroxide and ammonium carbonate in the first step of cation analysis?

Answer 19

To selectively precipitate some cations

Question 20

What is the color of the precipitate when Strontium Chromate (SrCrO₄) forms?

Answer 20

Yellow

Question 21

In the reaction scheme, which ion remains in the supernatant after the precipitation of SrCrO₄?

Answer 21

Ca²⁺

Question 22

When acetic acid and ammonium oxalate are added to the supernatant in the final step, what precipitate is formed?

Answer 22

Calcium oxalate

Question 23

What happens to the precipitate of magnesium ammonium phosphate (MgNH₄PO₄) in the reaction scheme?

Answer 23

It is discarded

Question 24

What is the purpose of centrifugation in the qualitative analysis of cations?

Answer 24

To separate the precipitate from the solution

Question 25

Why is heating required when testing for the presence of Strontium Chromate (SrCrO₄)?

Answer 25

To help form the yellow precipitate

Question 26

If no precipitate forms after adding ammonium oxalate in the final step, what does this indicate?

Answer 26

The solution does not contain Ca²⁺

Question 27

What would happen if potassium chromate was added at the beginning of the reaction instead of ammonium carbonate?

Answer 27

Ba²⁺ would precipitate immediately

Question 28

If a white precipitate forms upon adding ammonium oxalate, which ion is confirmed to be present?

Answer 28

Ca²⁺