In chemistry, a mole is a very large, fixed quantity, specifically $602,214,076,000,000,000,000,000($usually written as $6\mathrm{.}02214076\backslash$times $1023).$ The molar mass of a substance is the mass in grams of one mole of the substance $($grams $/$ mole$).$ A molar mass calculator is a program that computes the molar mass of a substance and the number of moles of a sample of that substance. To use a molar mass calculator, a chemist enters two inputs:

The formula for a molecule, such as H$2$O $($water$)$ or C$6$H$12$O$6($glucose$)$

The mass in grams of a sample of the substance, such as $3\mathrm{.}71$

The calculator computes the molar mass of the molecule by doing the following for each element in the formula:

Sum the number of atoms of each element in the formula

Find the atomic mass of each element

Multiply the number of atoms by their atomic mass

Add the product into the molar mass of the molecule

Then the calculator computes the number of moles in the sample with this formula:

number$\_$of$\_$moles $=$

sample$\_$mass

molar$\_$mass

Finally, the calculator prints two results for the chemist to see:

the molar mass

the number of moles

Example

As an example, consider a sample of glucose $($C$6$H$12$O$6)$ with a mass of $12\mathrm{.}37$ grams. To use a molar mass calculator, a chemist enters

C$6$H$12$O$6$

$12\mathrm{.}37$

The calculator computes the molar mass of glucose by doing the following:

Sum the number of atoms of each element in the formula for glucose:

$6$ carbon atoms

$12$ hydrogen atoms

$6$ oxygen atoms

Find the atomic mass of each element:

Symbol Name Atomic Mass

C Carbon $12\mathrm{.}0107$

H Hydrogen $1\mathrm{.}00794$

O Oxygen $15\mathrm{.}9994$

Multiply the number of atoms by their atomic mass:

$6\backslash$times $12\mathrm{.}0107=72\mathrm{.}0642$

$12\backslash$times $1\mathrm{.}00794=12\mathrm{.}09528$

$6\backslash$times $15\mathrm{.}9994=95\mathrm{.}9964$

Add the results of the multiplications to get the molar mass of glucose:

$72\mathrm{.}0642+12\mathrm{.}09528+95\mathrm{.}9964=180\mathrm{.}15588$ grams$/$mole

Then the calculator divides the mass of the sample of glucose by the molar mass of glucose which results in the number of moles in the sample:

$12\mathrm{.}37$ grams

$180\mathrm{.}15588$ grams$/$mole

$=0\mathrm{.}06866$ moles

The calculator prints two results for the chemist to see:

the molar mass of glucose: $180\mathrm{.}15588$ grams$/$mole

the number of moles in the sample: $0\mathrm{.}06866$ moles

Assignment

During this assignment, you will write and test the remaining parts of the molar mass calculator that you started writing in the previous lesson$$s prove milestone. When you are finished with this prove assignment, your chemistry.py program must contain at least three functions named as follows:

main

make$\_$periodic$\_$table

compute$\_$molar$\_$mass

Helpful Documentation

The prove milestone explains how a molar mass calculator should work.

The preparation content explains how to create and use a dictionary in a Python program.

The preparation content for week $3$ explains how to use pytest, assert, and approx to automatically verify that functions are correct. It also contains an example test function and links to additional documentation about pytest.

Download the formula.py Python file and save it in the same folder where you saved your chemistry.py program from the previous prove milestone. The formula.py file includes a FormulaError class and a function named parse$\_$formula. Both of them are complete and work correctly, and you should not change them.

Open the formula.py file in VS Code and read the triple quoted string at the top of the parse$\_$formula function. As the triple quoted string states, the parse$\_$formula function converts a chemical formula for a molecule, such as $"$C$13$H$16$N$2$O$2"($melatonin$),$ into a compound list, such as $[["$C$",13],["$H$",16],["$N$",2],["$O$",2]].$ This compound list is known as a symbol$\_$quantity$\_$list because it contains the symbols of chemical elements and the quantity of atoms of each element that appear in a chemical formula.

Copy and paste the following import statement into your chemistry.py program at the top of your program. This statement will import the parse$\_$formula function from the formula.py file into your chemistry.py program so that you can call the parse$\_$formula function in your program.

from formula import parse$\_$formula

In your chemistry.py program, change the compound list that is in your make$\_$periodic$\_$table function to a compound dictionary. Each item in the dictionary should have a chemical symbol as the key and the chemical name and atomic mass in a list as the value, like this:

periodic$\_$table$\_$dict $=\{$

# symbol: $[$name$,$ atomic$\_$mass$]$

$"$Ac$"$: $["$Actinium$",227],$

$"$Ag$"$: $["$Silver$",107\mathrm{.}8682],$

$"$Al$"$: $["$Aluminum$",26\mathrm{.}9815386],$

$$

$\}$

We strongly recommend that you use find and replace or multi$-$line editing in VS Code to quickly change the periodic table to a compound dictionary. If you don't know how to use find and replace or multi$-$line editing, ask a fellow student, a tutor, a teaching assistant, or your teacher for help.

Copy and paste the following Python code into your chemistry.py program. Be certain not to paste the code inside an existing function.

# Indexes for inner