# Tutor profile: Cecelia D.

## Questions

### Subject: Chemistry

Chlorine has a relative atomic mass of 35.45 g/mol. There also exists isotopes of chlorine, Cl-35 and Cl-37, each with the atomic masses of 34.97 and 36.97 g/mol, respectively. What is the relative abundance of Cl-37?

Consider this to be a simple algebra problem. X = abundance of Cl-35 Y = abundance of Cl-37 We know that: 34.97x + 36.97y = 35.45 x + y = 1 We want to solve for y. x = 1 - y, we then substitute in the top equation. 34.97(1 - y) + 36.97y = 35.45 Then simplify: 2y = 0.48 y = 0.24 The relative abundance of Cl-37 is 24%

### Subject: Basic Chemistry

Balance the following equation: _CO2 + _H2O -> _C6H12O6 + _O2

A good trick to balancing equations is to initially pick a molecule to have a coefficient of 1, then balance out the rest to be equal to it. For this, we will make C6H12O6 have coefficient of 1. We then look at CO2, which has 1 carbon, to make it balanced, there needs to be a coefficient of 6. Then H2O, which has 2 hydrogens, but to be equal to C6H12O6, also needs a coefficient of 6. We then have everything except for the number of O2 in the products. Add the number of O on the reactants side. This is 18. Then subtract the product we already know, C6H12O6, which has 6 oxygen atoms. This leaves 12, but since it is O2, you must divide by 2, which leaves you with 6. The balanced equation is then: 6CO2 + 6H2O -> C6H12O6 + 6O2

### Subject: Biology

Name three skeletal features that distinguished mammals from their now-extinct ancestors, synapsids.

Mammals are known for their enlarged dentary bone (mandible), whereas synapsids had several smaller bones as part of their jaw, specifically used for articulation. Mammals also have dentary-squamosal articulation, while synapsid jaw articulation occurred with smaller bones known as the quadrate and articulate. These bones shifted in mammals to their inner ear. Mammals have 3 ossicles (inner ear bones) and the synapsids just had one, the stapes.

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