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# Tutor profile: Catherine A.

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Catherine A.
Chemistry major with experience tutoring General Chemistry and Math
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## Questions

### Subject:Pre-Algebra

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Question:

Solve the following expression for x: 7 = x + 3.

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Catherine A.

First, rewrite the equation: 7 = x + 3. Note that we want to isolate x, so we subtract 3 from both sides: 7 - 3 = x + 3 - 3. The +3 and -3 on the right side cancel out to give zero, so we obtain 7 - 3 = x. Then, simply perform the subtraction on the left side of the equation to obtain that 4 = x.

### Subject:Chemistry

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Question:

Write both the full and shorthand electronic configurations for the ion \$\$Cl^{-1}\$\$.

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Catherine A.

First, note that the chlorine ion has a charge of -1, indicating that there is one additional electron associated with it. Therefore, when determining the electron configuration, you must go to the next highest element on the table after Cl, which is Ar. For the full configuration, note that each element box on the table represents 1 electron, and be aware of where s,p,d, and f orbitals are represented on the table. Thus, beginning with H, the electron configuration is: \$\$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}\$\$. Each number in front of a letter represents the level on the periodic table (the shell). The shorthand notation uses the noble gas that is before the desired table location, followed with the remaining electrons. This gives an answer of: \$\$[Ne]3s^{2}3p^{6}\$\$.

### Subject:Basic Chemistry

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Question:

Consider the compound calcium carbonate. Write the chemical formula of this compound and determine its molecular weight in g/mol. If you must obtain 0.56 g of calcium carbonate, how many moles is this quantity?

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Catherine A.

The chemical formula of this compound is \$\$CaCO_{3}\$\$. This is because the calcium ion has a charge of +2, and the carbonate ion has a charge of -2. To determine the molecular weight, consider each atom directly, with its mass from the periodic table. Multiply this by the number of those atoms in the compound, as follows: Ca: 1 * 40.08 g/mol C: 1 * 12.01 g/mol O: 3 * 15.99 g/mol Now, add these values: 40.08 g/mol + 12.01 g/mol + 47.97 g/mol = 100.06 g/mol Finally, use stoichiometry to convert the gram amount to moles, keeping the correct significant figures: (0.56 g)(1 mol/ 100.06 g) = 0.0056 moles

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