HESI A2 ENTRANCE EXAM CHEMISTRY QUESTIONS AND VERIFIED ANSWERS 2023

A mystery element has 6protons,6 electrons and 6neutrons.What is its atomic number? • 6 • 12 • 18 • Not enough information The correct answer is A. An atom can always be identified based on the number of protons which will always be the same for atoms of the same element. The atomic number is always equal to the number of protons. • Amysteryelementhas13 protons,13 electrons and 14neutrons.What element is it? • Fe • Zr • Al • Notenoughinformation The correct answer isC. Atoms can always beidentifiedwith the number ofprotons. Sincethis atomhas13protons, theatomicnumber is 13,whichisaluminum. • What are buffers? • Proteins • Solutions that resist changes in pH • Catalysts in a reaction • Inhibitors in a reaction The correct answer is B. Buffers resist change in pH and are key to maintaining stableH+ ionconcentrations. • What does carbonic aciddowithinthehumanbody? • Digestsfood • Killsviruses • MaintainspHofblood The correct answer is C. Carbonic acid is a buffer that maintains the pH of human blood. Other acids are presentinthe stomach in order to digest food. Use the following chemical reaction to answer the following questions: • What are the reactants? • CH4and O2 • CO2and H2O ThecorrectanswerisA.Thereactantsarealwaysontheleftsideofareactionandaret heatomsormoleculespresentatthestart ofareaction. • Whataretheproducts? • CH4and O2 • CO2and H2O • Both • Noneoftheabove ThecorrectanswerisB.Productsaremadebyreactions andarealwaysontherightsideofthearrow. • Howmanyhydrogenatoms arepresentinthereactants? • 2 • 4 • 1 • Noneoftheabove ThecorrectanswerisB.Thesubscript4aftertheHsymbolindicatesthatthereare4at omsofhydrogeninCH4. • Howmanyoxygenatomsare in2O2? • 2 • 4 • 1 • 0 The correct answer is B. The normal sized 2 is called a coefficient. It meansthat there are twomolecules of whatever comes after it, in this case there are 2 molecules of O 2. O2 has 2 atoms of oxygenand the coefficient of 2 means that there would be 4 total oxygen atoms. Coefficients are similar todistributing in algebra. All subscript numbers involved in the compound are multiplied by the coefficientamount. • Howmanywatermolecules arepresentintheproducts? • 2 • 4 • 1 • 0 The correct answer is A. The coefficient of 2 before the water molecule indicates that there are 2 of thatmolecule.