CHM 101/FSC 112: Errors, Accuracy, and Stoichiometry

A student measures the mass of a sample three times and obtains the following values: 15.5 g, 15.6 g, and 15.7 g. The true mass of the sample is known to be 16.8 g. Which statement best describes the student's measurements?

In a laboratory experiment, four students each made three measurements of the length of a metal rod. The actual length of the rod is 25.0 cm. Which student's measurements display both high accuracy and high precision?

A chemist performs an experiment to determine the concentration of a solution. Which scenario indicates the presence of systematic error?

A student weighs a sample on a balance and records the mass as 10.25 g. Later, the student discovers that the balance was not calibrated correctly and consistently reads 0.05 g too high. What type of error is this?

What is the term for the extent to which repeated measurements yield the same result?

In a chemical reaction, the theoretical yield of a product is 25.0 grams. A student performs the reaction and obtains 20.0 grams of the product. What is the percent yield?

A chemist measures the mass of a compound to be 5.00 g, but the true mass is 5.20 g. Calculate the absolute error.

The accepted value for a standard solution's concentration is 0.100 M. A student performs an experiment and obtains a value of 0.095 M. Calculate the percent relative error.

A goldsmith weighs a piece of gold and records a weight of 1.45 g, but its actual weight is 1.50 g. Calculate the relative error.

Three students independently perform the same experiment to determine the density of a metal. Their results are: Student 1: 7.85 g/mL, Student 2: 7.88 g/mL, Student 3: 7.82 g/mL. If the true density of the metal is 7.84 g/mL, which statement is most accurate?

What is the purpose of using carbon-12 ($^{12}C$) as the standard for determining relative atomic masses?

Why is the average atomic mass of carbon listed as 12.01 amu on the periodic table, rather than exactly 12 amu?

Chlorine has two isotopes: $^{35}Cl$ with a mass of 34.968 amu and $^{37}Cl$ with a mass of 36.956 amu. If the relative abundance of $^{35}Cl$ is 75.77% and $^{37}Cl$ is 24.23%, what is the average atomic mass of chlorine?

What is the definition of a 'mole' in chemistry?

What is the approximate value of Avogadro's number?

How many hydrogen atoms are present in 0.75 mol of $C_6H_{12}O_6$?

What is the molar mass of methane ($CH_4$)? (Atomic mass: C = 12.01 amu, H = 1.008 amu)

If a sample has a mass of 46 grams and its molar mass is 92 g/mol, how many moles are in the sample?

What is the percentage composition of carbon in ethanol ($C_2H_5OH$)? (Molar mass: C = 12.01 g/mol, H = 1.008 g/mol, O = 16.00 g/mol)

Determine the percentage composition of oxygen in sodium oxalate ($Na_2C_2O_4$). (Molar mass: Na = 22.99 g/mol, C = 12.01 g/mol, O = 16.00 g/mol)

Which of the following is a valid unit for molar mass?

A reaction requires 2.0 moles of reactant A (molar mass = 50 g/mol). What mass of reactant A is needed?

Given the reaction: $2H_2 + O_2 → 2H_2O$. If 4.0 grams of $H_2$ react completely, how many grams of $H_2O$ are produced? (Molar mass: $H_2$ = 2.0 g/mol, $H_2O$ = 18.0 g/mol)

Consider the following balanced equation: $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$. If you start with 6.022 x $10^{23}$ molecules of $N_2$, how many molecules of $NH_3$ can be produced, assuming excess $H_2$?

For the reaction $2CO(g) + O_2(g) \rightarrow 2CO_2(g)$, if you have 4 moles of CO and 3 moles of $O_2$, which reactant is the limiting reactant?

In the reaction $A + 2B \rightarrow C$, if the molar mass of A is 20 g/mol and the molar mass of B is 10 g/mol, what mass of B is required to completely react with 10 g of A?

A compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

A compound has an empirical formula of $CH_2O$ and a molar mass of 180 g/mol. What is its molecular formula?

If 5.0 g of methane ($CH_4$) is completely combusted, what mass of carbon dioxide ($CO_2$) is produced? (Molar mass: CH4 = 16 g/mol, CO2 = 44 g/mol)

Consider the reaction: $2A + B \rightarrow C$. If 100 g of A (molar mass 25 g/mol) reacts with 80 g of B (molar mass 40 g/mol), which reactant is limiting?

If the percentage composition of hydrogen in a compound is 2.016%, and the molar mass of the compound is 100 g/mol, what is the mass of hydrogen in one mole of the compound?

In mass spectrometry, what causes ions with lower molecular weight to deflect more than ions with higher molecular weight?

Using the diagram showing targets, which of the following best describes 'Jane's' shooting?

What distinguishes relative error from absolute error in measurements?

Why is it important to distinguish between accuracy and precision in scientific measurements?

How does the mass spectrometer differentiate between isotopes of the same element?