Q1. If the density of an object is 3.0 mg/L, what is the density in g/mL?

Background

Topic: Unit Conversions (Density)

This question tests your ability to convert between different units of density, specifically from milligrams per liter (mg/L) to grams per milliliter (g/mL).

Key Terms and Formulas:

• Density:

• Unit conversions: ,

Step-by-Step Guidance

1. Start by writing the given density: .

2. Convert milligrams to grams: , so multiply the value by to get grams.

3. Convert liters to milliliters: , so divide the value by $1000$ to get per milliliter.

4. Combine the conversions to express the density in .

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Q2. Report the answer to the following computation to the correct significant figures: 1.68 - 3.719

Background

Topic: Significant Figures in Calculations

This question tests your understanding of how to apply significant figure rules when performing subtraction.

Key Terms and Formulas:

• Significant Figures: The digits in a measurement that are known with certainty plus one that is estimated.

• For addition/subtraction: The result should be reported to the same decimal place as the least precise measurement.

Step-by-Step Guidance

1. Write the numbers vertically, aligning the decimal points:

2. Perform the subtraction without rounding yet.

3. Determine the number of decimal places in each value: has two decimal places, has three.

4. The answer should be rounded to the least number of decimal places (two, in this case).

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Q3. What is Ar classified as?

Background

Topic: Periodic Table Classification

This question tests your knowledge of the periodic table and the classification of elements, specifically argon (Ar).

Key Terms:

• Noble gases: Group 18 elements, inert and nonreactive under standard conditions.

• Halogens: Group 17 elements, highly reactive nonmetals.

• Metalloids: Elements with properties intermediate between metals and nonmetals.

• Metals: Elements that are typically shiny, conductive, and malleable.

Step-by-Step Guidance

1. Locate argon (Ar) on the periodic table. Identify its group number.

2. Recall the properties of elements in that group.

3. Match those properties to the correct classification (noble gas, halogen, etc.).

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Q4. Potassium carbonate reacts with a solution of hydroiodic acid. What is the nature of the gas evolved?

Background

Topic: Chemical Reactions – Gas Evolution

This question tests your understanding of double displacement reactions and the identification of gases produced during acid-carbonate reactions.

Key Terms and Concepts:

• Potassium carbonate:

• Hydroiodic acid:

• Acid-carbonate reactions typically produce carbon dioxide gas ().

Step-by-Step Guidance

1. Write the balanced chemical equation for the reaction between and .

2. Identify the products formed, focusing on any gas produced.

3. Recall the general pattern: carbonate + acid → salt + water + carbon dioxide gas.

4. Determine the nature (identity) of the gas evolved based on the reaction type.

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Q5. A compound contains 1.2 g of C and 0.24 g H. What is the empirical formula?

Background

Topic: Empirical Formula Determination

This question tests your ability to determine the simplest whole-number ratio of atoms in a compound from mass data.

Key Terms and Formulas:

• Empirical formula: The simplest ratio of elements in a compound.

• Moles:

• Molar mass of C: ; H:

Step-by-Step Guidance

1. Calculate the number of moles of C:

2. Calculate the number of moles of H:

3. Divide both mole values by the smallest number of moles to get the simplest ratio.

4. If necessary, multiply both numbers by a small integer to get whole numbers.

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