Midterm Chemistry Quiz

What is the missing coefficient for oxygen gas (O₂) in the balanced equation? C₄H₁₀ + O₂ → CO₂ + H₂O

• 5

• 6

• 8

• 10

A student incorrectly balances an equation by changing subscripts instead of coefficients. Why is this incorrect?

• It violates the Law of Conservation of Energy

• It changes the identity of the substances involved

• It only works for synthesis reactions

• It does not affect the equation

Tags

NGSS.HS-PS1-7

If 4.5 moles of H₂ react with excess oxygen, how many moles of H₂O are produced? 2H₂ + O₂ → 2H₂O

• 2.25 moles

• 4.5 moles

• 6.75 moles

• 9.0 moles

Tags

NGSS.HS-PS1-7

A chemical reaction follows a 3:2 ratio of reactants. If a student starts with 12.0 moles of one reactant, how many moles of the other reactant are needed?

• 4.0 moles

• 8.0 moles

• 12.0 moles

• 18.0 moles

In a lab experiment, a student combines 15.0 g of aluminum with excess oxygen. The theoretical yield of aluminum oxide is 28.3 g. If the actual yield is 25.1 g, what is the percent yield?

• 74.2%

• 88.7%

• 93.1%

• 98.6%

Tags

NGSS.HS-PS1-7

When determining the limiting reactant, what is the first step?

• Convert reactants to mass

• Convert reactants to moles

• Divide the given mass by the molar mass

• Predict the reaction products

Which combination of reactants will result in a precipitate?

• NaCl + KNO₃

• MgCl₂ + AgNO₃

• HCl + NaOH

• CuSO₄ + Na₂SO₄

If two aqueous solutions are mixed and a precipitate forms, what conclusion can be made?

• A new compound is formed, but no reaction occurred

• The reaction resulted in an insoluble product

• The solution has reached its boiling point

• The reactants evaporated

A radioactive element undergoes beta decay. How does the nucleus change?

• A neutron is converted into a proton

• Two protons are lost

• The atomic number decreases by 2

• The mass number decreases by 4

Tags

NGSS.HS-PS1-8

If a radioactive isotope has a half-life of 10 years, how much remains after 30 years if you start with 80 g?

• 40 g

• 20 g

• 10 g

• 5 g

Tags

NGSS.HS-PS1-8