May 2009

MULTIPLE CHOICE SECTION: The May of 2009 CORE 40 test will contain  50 multiple choice questions.  Each student will have access to a PACKET of questions which have been specifically designed to prepare students for the Chemistry CORE 40 exam.  In class, students will work individually or in small groups working on the questions.  Answers to the PACKET questions will also posted here.  In addition to the answers, each question has a specific page reference along with the identified Chemistry standard.

PROBLEMS SECTION:  

The last part of the Chemistry CORE 40 contains problems which will likely come from the topics listed below. 

• These are problems which test your fundamental understanding of the nature of matter and test whether you can utilize appropriate math skills to solve mathematics-based chemistry problems. 
• BRING YOUR NON-GRAPHING CALCULATOR TO CLASS EVERY DAY AND FOR THE FINAL EXAM.
• For the exam, students will be receiving a stapled set of "reference sheets". 

See helpful hints below:

1. Substances (elements and compounds) and the fundamental characteristics of the phases of matter.  

Hint: This concept tested will also include:

• knowing the difference between a solid, liquid and gas (in terms of particles)
• knowing the difference between an atom and an ion
• knowing the difference between covalent and ionic compounds
• knowing the difference between homogeneous mixtures and heterogeneous mixtures
• knowing the difference between physical changes and chemical changes

2. Reaction prediction and balancing chemical equations.

Examples:
Aluminum plus nitrogen ®
Sodium carbonate ®
Nickel (II) chloride plus ammonium sulfide ®
Scandium plus hydrochloric acid ®

Hint: Be sure to have memorized all the types of reaction prediction types. In addition, you'll need to be able to write formulas correctly and balance equations in order to receive full credit for these problems.

Hint: It is also likely that you will have stoichiometry problems which ALSO involve first writing the balanced chemical equation (like above).

3. Percent composition, empirical and molecular formula determination.

Example:
For the compound, magnesium phosphate, calculate the % composition for each element present.
For a compound containing 40.00% C, 6.72% H, 53.29% O, determine the empirical formula.
For this same compound, if 0.1 mole = 18 g for the substance, determine the molecular formula.

4. Stoichiomentry (including limiting reactants) - FOCUS ON THESE TYPES OF PROBLEMS.

Example: Calcium reacts completely with 100 mL of a .20 M aqueous solution of HCl to produce hydrogen gas and an aqueous solution. How many grams of calcium was consumed?

Example: 25 g of magnesium nitrate reacts with an excess of calcium carbonate.  Find how much magnesium carbonate is produced.

Hint: Be sure to write and balance the chemical reaction first. Then, use the molar connection in your dimensional analysis.

Example: 17 grams of methane are allowed to react with 20 grams of oxygen. Find the mass of water produced.

Hint: You'll need to set up two dimensional analyses  in order to determine the correct answer. Pay attention to sig figs.

5. Gas Laws.

Example: 15.0 L of a gas is found to exert 97.0 kPa at 25.0°C. If the volume stays constant, what would be the required temperature (in Celsius) to change the pressure to standard pressure? (Hint: You need to know what standard pressure is...)

 

PRACTICE PROBLEMS DURING CLASS