AP Chemistry Question of the Day --2

Here comes the answer to question 1  I posted yesterday. The correct answer is C.
Atom is the smallest unit that retain the properties of the individual element. Each atom consists of a nuclear and electron(s) surrounding the nuclear. The nuclear is very dense and takes up only a tiny portion of the total volume of the atom. The vast space outside the nuclear is empty and electrons move around in it. In the nuclear, there are protons and neutrons. The number of protons are called the atomic numbers. Each element in the periodic table has a characteristic atomic number, which is the same as the protons in the nuclear. Each proton carries a charge of +1.  Neutrons are neutral and carry no charge. The number of electrons orbiting the nuclear is the same as the atomic number when the atom is neutral. Atoms of the same element can have different number of neutrons. They are called isotopes. For each isotope, the mass of the atom is roughly the total number of protons and neutrons in the nuclear since electrons have negligible mass compared to proton and neutron. The atomic mass we observe from the periodic table is the weighted mass of all the naturally occuring isotopes of that element. It is calculated as follows which is the sum of the product of the mass of each isotope and its abundance:

In Question 1, we know the weighted average is 35.5 and we know the mass of the two major isotopes are 35 and 37. Assume 35Cl is x%, then

which gives x to be 66%.

Following is AP Chemistry Question of the Day --2:

2. Relatively slow rates of chemical reaction are associated with which of the following:

A. The presence of a catalyst
B. High Temperature
C. High concentration of reactants
D. Strong bonds in reactant molecules


I will post the answer and explanation tomorrow.

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