# Tutor profile: Joy L.

## Questions

### Subject: Chemistry

Balance the following reaction: Al + HCl -> AlCl3 + H2

The goal of this problem is to have all the elements balanced on either side of the reaction equation. To start, pick an element to start. It is probably good to start with Cl because it has 3 moles on the right and 1 mole on the left. To balance this, the coefficient of 3 should be placed next to HCl: Al + 3HCl -> AlCl3 + H2. Now, since there is a 3 on HCl, there are three H's on the left while there are 2 on the right. To balance this, we can change 3 HCl to 6 and the the coefficient of H2 on the left should be changed to 3. So now, there are 6 H's on both sides. Changing 3 to 6 on HCl changes the amount of Cl (now there are 6 on the left and 3 on the right). Then, we can make the coefficient of AlCl3 on the right to 2 so that there are 6 Cl's on either side. Now, there are 2 Al's on the right and 1 on the left. We can change the Al coefficient on the left to 2. Thus, the final equation would be 2 Al + 6 HCl -> 2AlCl3 + 3H2. It is important to check. There are 2 Al's on either side, there are 6 H's on either side, and there are 6 Cl's on either side.

### Subject: Biology

What is the complementary DNA strand for the following polypeptide sequence: 5'ATCGTATTAGC3'

First, the DNA strand template given goes from 5' to 3', so the complementary strand will go the opposite from 3' to 5'. The answer must have this direction written. The complementary strand pairings are A-T and G-C (vise versa). So, the final answer must be: 3'TAGCATAATCG5'

### Subject: Calculus

Find dy/dx of the following equation: x^2 + 4x +5

To take the derivative of a variable that has an exponent, the exponent is brought to the front of the variable and the current exponent is decreased by one. So, x^2 becomes 2x; 4x becomes 4; 5 becomes 0 (because there is no variable). Thus, the answer is 2x + 4