What color do acids make litmus paper turn?

A. Red

B. Yellow

C. Blue

D. Black

Answer Explanation:

A) Red (Correct Answer): Acids turn litmus paper red. Litmus paper is a common indicator that changes color in response to changes in acidity or alkalinity. Acids change the blue litmus paper to red.

B) Yellow: Acids do not typically turn litmus paper yellow. Litmus paper is generally unaffected by acids in a way that would cause it to turn yellow.

C) Blue: Acids do not turn litmus paper blue. Instead, they change blue litmus paper to red.

D) Black: Acids do not turn litmus paper black. Litmus paper is not expected to change to black in the presence of acids.

Therefore, the Correct Answer is A.

Q #1: How would you remove unreacted copper oxide from solution?

A. Filtration

B. Distillation

C. Evaporation

D. Decantation

Answer Explanation

A) Filtration (Correct Answer): Filtration is a commonly used method to separate solid particles, such as unreacted copper oxide, from a liquid solution. The solution containing the dissolved copper sulfate can pass through the filter paper, while the solid copper oxide particles are retained on the filter.

B) Distillation: Distillation is a process used to separate components of a mixture based on differences in their boiling points. It is not typically used to separate solid particles from a liquid solution.

C) Evaporation: Evaporation involves heating the solution to allow the solvent (water) to vaporize, leaving behind the solute (copper sulfate) as solid crystals. While evaporation can concentrate the solution, it does not effectively remove solid particles like unreacted copper oxide.

D) Decantation: Decantation involves pouring off the liquid portion of a mixture, leaving the solid behind. While it can be used to separate solid and liquid phases, it may not effectively separate fine solid particles like unreacted copper oxide from the solution. Filtration would be a more suitable method for this purpose.
Q #2: Why is NaCl neutral?

A. Because it contains both hydrogen and hydroxide ions in equal amounts

B. Because it contains hydrogen ions (H+) and hydroxide ions (OH-) in equal amounts

C. Because it does not contain any hydrogen or hydroxide ions

D. Because it dissociates completely in water

Answer Explanation

Rationale for each choice:

A) Because it contains both hydrogen and hydroxide ions in equal amounts: This statement is incorrect. NaCl (sodium chloride) does not contain hydrogen or hydroxide ions. It dissociates into sodium ions (Na+) and chloride ions (Cl-) in water, not hydrogen or hydroxide ions.

B) Because it contains hydrogen ions (H+) and hydroxide ions (OH-) in equal amounts: This statement is incorrect. NaCl does not contain hydrogen or hydroxide ions. In aqueous solution, NaCl dissociates into sodium ions and chloride ions, not hydrogen or hydroxide ions.

C) Because it does not contain any hydrogen or hydroxide ions (Correct Answer): NaCl is a neutral compound composed of sodium ions (Na+) and chloride ions (Cl-). It does not contain any hydrogen or hydroxide ions, so it is neutral in aqueous solution.

D) Because it dissociates completely in water: NaCl does dissociate in water, but its dissociation does not involve the generation of hydrogen or hydroxide ions. It dissociates into sodium ions and chloride ions, which do not contribute to the pH of the solution. Therefore, the completeness of dissociation does not determine its neutrality.
Q #3: What is a precipitate?

A. A gas formed during a chemical reaction

B. A liquid formed when two aqueous solutions react

C. A solid formed when two aqueous solutions react

D. A solution formed during a chemical reaction

Answer Explanation

A) A gas formed during a chemical reaction: While gases can indeed be produced during chemical reactions, a precipitate specifically refers to a solid that forms during a reaction.

B) A liquid formed when two aqueous solutions react: Precipitates are not liquids. They are solids that are formed when certain ions combine to form an insoluble compound.

C) A solid formed when two aqueous solutions react (Correct Answer): A precipitate is indeed a solid substance that forms when two aqueous solutions react and certain ions combine to create an insoluble compound.

D) A solution formed during a chemical reaction: A precipitate is not a solution. It is the solid product that separates out of a solution during a chemical reaction due to its limited solubility.

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What color do acids make litmus paper turn?

More Questions on TEAS 7 Science

Q #1: How would you remove unreacted copper oxide from solution?

Answer Explanation

Q #2: Why is NaCl neutral?

Answer Explanation

Q #3: What is a precipitate?

Answer Explanation

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