Halide Ions Test Quiz

In the test for halide ions, explain why nitric acid (rather than other acids) is added to a sample before you add silver nitrate solution.

• Nitric acid prevents the formation of other precipitates that could interfere with the test results.

• Nitric acid reacts with halide ions to produce a colored gas.

• Nitric acid increases the solubility of silver nitrate in water.

• Nitric acid neutralizes the halide ions, making them undetectable.

Scientists might choose to use instruments to analyze a sample instead of relying on traditional chemical tests because:

• Instruments provide more accurate and reliable results, and can analyze smaller sample sizes.

• Traditional chemical tests are always faster and more precise than instruments.

• Instruments are only used because they are cheaper than traditional tests.

• Traditional chemical tests do not require any reasoning or planning.

One potential disadvantage of using instruments for chemical analysis in a laboratory is:

• Instruments can be expensive to purchase and maintain, and may require specialized training to operate.

• Instruments always give incorrect results compared to traditional tests.

• Instruments are never used in modern laboratories.

• Traditional chemical tests are more expensive than instruments.

A laboratory is considering whether to use instrumental analysis for testing a new drug. The lab has a limited budget, but needs highly accurate results and only has a very small sample of the drug. Based on the benefits and disadvantages of instrumental analysis, what should the lab consider before making a decision?

• Instrumental analysis is inexpensive and does not require special training.

• Instrumental analysis is highly accurate and can analyze small samples, but it is expensive and requires special training.

• Instrumental analysis is slow and cannot analyze small samples.

• Instrumental analysis can only be used for unknown substances.

A scientist needs to compare the results of an unknown sample with a database of known substances. Why might instrumental analysis be limited in this scenario, and what reasoning should the scientist use to decide if this method is appropriate?

• Instrumental analysis can only compare results with known samples, so it may not help if the unknown is not in the database.

• Instrumental analysis is always the best method for unknown substances.

• Instrumental analysis is not accurate enough for any comparison.

• Instrumental analysis is only used for large samples.

Imagine you are planning a research project that requires quick results and only a tiny amount of material is available for testing. What strategic reasoning would support the use of instrumental analysis, and what potential challenges should you plan for?

• Instrumental analysis is slow and requires large samples, so it is not suitable.

• Instrumental analysis is quick and can analyze small samples, but you must plan for high costs and the need for specialized training.

• Instrumental analysis is cheap and easy to use for any sample size.

• Instrumental analysis does not require any planning or special considerations.

A chemist is given an unknown sample and asked to identify which metal ion it contains using flame emission spectroscopy. Which of the following is a strategic approach the chemist could use to determine the identity of the metal ion, considering the similarities and differences with traditional flame tests?

• The chemist should compare the color of the flame produced by the unknown sample to a reference chart of known metal ion flame colors, and use additional evidence from the emission spectrum to confirm the identity.

• The chemist should only rely on the color of the flame without any further analysis.

• The chemist should mix the sample with water and observe any changes.

• The chemist should use only the boiling point of the sample to identify the metal ion.

Flame emission spectroscopy can help a chemist distinguish between sodium (Na⁺) and potassium (K⁺) ions because:

• Flame emission spectroscopy provides a unique emission spectrum for each metal ion, allowing the chemist to distinguish between sodium and potassium even if their flame colors are similar.

• Flame emission spectroscopy only shows the same color for all metal ions, making it unreliable.

• The chemist should ignore the emission spectrum and rely on taste.

• The chemist should use the melting point of the sample instead.

Explain how the process of flame emission spectroscopy allows scientists to identify elements in a sample. Use reasoning to connect the excitation and de-excitation of electrons to the emission of light.

• The color of light emitted is unique to each element because electrons release specific amounts of energy when they return to lower energy levels.

• The sample is heated so that it melts and forms a new compound, which emits light.

• The electrons are removed from the atom, causing the atom to glow.

• The nucleus emits light when it absorbs energy from the flame.

A scientist observes a specific color of light emitted from a heated sample during flame emission spectroscopy. What reasoning process should the scientist use to determine which element is present in the sample?

• Compare the observed color to known emission spectra of elements to identify the element.

• Measure the temperature of the flame to determine the element.

• Weigh the sample before and after heating to identify the element.

• Observe the shape of the sample to determine the element.