# Tutor profile: Allison K.

## Questions

### Subject: Chemistry

After experimentation it is found that $$12.3 mL$$ of $$0.613 M NaOH(aq)$$ is needed to neutralize $$17.4 mL$$ of an $$H_{2}SO_{4}(aq)$$ solution. Determine the molarity of the $$H_{2}SO_{4}.$$

This question involves a titration between a strong acid and strong base. In questions like these, the first thing we always have to do is write out a balanced chemical equation. For this reaction, the equation would be: $$2NaOH(aq) + H_{2}SO_{4}(aq) -> Na_{2}SO_{4}(aq) + 2H_{2}O(l)$$. The equation relating molarity (M), moles (mol), and volume (L) is as follows: $$M=\frac{mol}{L}$$. Because the above equation involves the titration of a strong acid and base, the moles of acid can be related to the moles of base using their stiochiometric ratios. The equation shows us that for every 2 moles of base, there is one mole of acid. Keeping this in mind, we can solve for the moles of base ($$NaOH(aq)$$) by rearranging the formula for molarity to be $$mol=(M)(L)$$. We use the given information to substitute into the equation (ensuring that we convert the mL to L first). $$mol=(0.0123L)(0.613M)= 0.0075399mol NaOH(aq)$$. Now that we have the moles of base, we can find the moles of acid by dividing this number by 2-because, as we realized before, the moles of acid are half of the moles of base. $$0.0075399mol NaOH(aq)/2=0.00376995 mol H_{2}SO_{4}(aq)$$. Now that we know the moles of acid, we can re-substitute into our original equation to find molarity: $$M=\frac{0.00376995 mol}{0.0174L}=0.2166637931M H_{2}SO_{4}(aq)$$. Rounding to the correct number of significant figures, we get our final answer: $$0.217M H_{2}SO_{4}(aq)$$.

### Subject: Basic Chemistry

Use the periodic table to determine the number of electrons in a neutral atom of oxygen.

If we look at the periodic table, we see that oxygen (O) the eighth element listed. To find the number of electrons in an atom, we have to pay attention to the atomic number of the element. The atomic number is found above the symbol of each element, and it indicates the number of protons in the element. For oxygen, this number is 8. This means that in the nucleus of an oxygen atom, there are 8 positively charged subatomic particles. Because the atom of oxygen being asked about is neutral, it means that it has no charge. For an atom to have no charge, the number of electrons (negatively charged particles) must equal the number of protons (positively charged particles), because the opposite charges will cancel one another out. So, within a neutral oxygen atom there are 8 electrons.

### Subject: Algebra

Solve for x: 6(4x-9)+5x=12

First, we have to distribute the term outside of the parenthesis to each term inside of the parenthesis. If we do this, we multiply to get $$ 24x-54+5x=12. $$ Next, we have to add like terms: here, we have two terms with $$x$$ in them, so we add those to get $$ 29x-54=12.$$ We now want to get the variables alone on one side of the equation (in other words, we have to move $$-54$$ to the other side of the equal sign). To do this, we add $$54$$ to both sides. On the left side of the equation, the $$-54$$ and $$+54$$ cancel one another out, and on the right side, we add $$54$$ and $$12$$ to get $$66.$$ The equation now looks like this: $$29x=66$$ As our last step, we have to isolate $$x$$ to obtain its value. To do this, we divide both sides of the equation by the coefficient of $$x$$ (the number in front of it), which is $$29$$. Doing this, we get our answer to be $$x=66/29.$$

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