# Tutor profile: Fiona M.

## Questions

### Subject: Basic Chemistry

C3H8 reacts with O2 to form H20 and CO2. If 2 equivalents of C3H8 are used, how many equivalents of O2 are needed to fully react the compound?

First, we need to count the number of atoms we know are on each side of the reaction. On the reactants side we have 6 C's (because there are two molecules, so we take two times however many atoms are in the molecule), and 16 H's. On the product side, we need to balance those same number of atoms. To use up all 16 H's, we would need 8 equivalents of H2O. To use up the 6 C's, we need 6 equivalents of CO2. Now, count the number of oxygen atoms needed to make the products. For the 8 H2O, we need 8 O's. For the 6 CO2, we need 12 O's. In total, there needs to be 20 O's reacted. Since the reactant oxygen is O2, we need 10 equivalents of O2 to get the necessary 20 O's. The final reaction equation looks like this: 2 C3H8 + 10 O2 -> 8 H2O + 6 CO2

### Subject: Biology

A couple visits a genetic counselor to determine their chance of having a child with Disease K, which is an autosomal recessive disease. The wife has a sibling with Disease K, but no one else in her immediate family shows the phenotype. What is the probability that the wife is a carrier of a Disease K allele?

Since the wife has a sibling with Disease K, we know that both of her parents must be carriers. The parents do not show the disease phenotype, so neither of them has two Disease K alleles, meaning that they are both heterozygous for the allele. Given the genotype of the parents, their offspring have a 25% chance of having two disease alleles, a 50% chance of carrying only one disease allele, and a 25% chance of carrying no disease alleles, following a 1:2:1 ratio. The wife does not have Disease K, so we know that she does not fall into the 25% with both alleles. This leaves the other two options, the percentages of which need to be normalized to remove the 25% we just ruled out. Therefore, the new ratio becomes 2:1 (heterozygous carrier:no allele). Expressed in a percentage, the wife has a 66 2/3% chance of carrying one Disease K allele.

### Subject: Physics

Is an elevator moving upwards at a constant speed an inertial frame of reference? Is an elevator orbiting Earth at a constant speed an inertial frame of reference? Why or why not?

An inertial frame of reference is achieved when an object is experiencing constant velocity, which is speed in a given direction. Therefore, an elevator moving upwards at a constant speed IS an inertial frame of reference because the velocity does not change; both the speed and the direction stay constant. The elevator orbiting Earth at a constant speed IS NOT an inertial frame of reference because it is accelerating due to the circular orbit it is traveling; although the speed stays constant, the direction is constantly changing to account for the circular motion.

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