Science lab concentration | Chemistry homework help
- Take a cup of water, add sugar, and stir. If the resulting solution contains sugar crystals that do not
dissolve, is the solution saturated or unsaturated? Unsaturated - If there is no precipitate at the bottom then it is likely less than the maximum amount of the solute is present. ----------------------------------------------------------------------------------------------------------------------------- Concentration PHSC 1021 online 2 | P a g e Moles and Molarity In addition to the broad categories of saturated and unsaturated, solutions can be classified based on their concentration or molarity. Molarity is the concentration of a solution expressed in the number of moles of solute per liter of solution. In order to calculate the molarity of a solution, you need to know the number of moles of solute and the total volume of the solution. Moles are used to measure the amount of a substance. A mole is a number of somethings. The same way a dozen eggs means twelve eggs. A mole of atoms is 6.02x1023 atoms. For this lab we will focus on a property of moles concerning mass. To understand this property of moles, first we will talk about atomic mass and formula mass. Chemical Formula and Number of Atoms Compounds such as sodium chloride and water can be written out as words or a shorthand form of the name can be written. This shorthand form is called the chemical formula. Look back at figure 1 and notice that H2O is used instead of water. In the same figure NaCl is used instead of sodium chloride. The chemical formula for a substance contains the chemical symbol for each element present. If there is more than one atom of that element then a subscript will also be used in the chemical formula. The subscripts show the number of atoms of that element. If there is a subscript 2, that means the compound contains two atoms of that element. A subscript of 3 would mean the compound contains three atoms of that element. H2O has two hydrogen atoms and one oxygen atom. NaCl has one sodium atom and one chlorine atom. Copper(II) sulfate, CuSO4, has one copper atom, one sulfur atom, and four oxygen atoms. The purpose of the chemical formula is to have a shorthand way of describing the compounds. Cobalt (II) nitrate has the chemical formula Co(NO3)2. This signifies that one cobalt atom is bonded to two nitrate ions. If we are counting atoms and parentheses are present, then we multiply the subscript times everything in the parentheses. Therefore cobalt(II) nitrate has one cobalt atom, 2x1=2 nitrogen atoms, and 2x3=6 oxygen atoms. -----------------------------------------------------------------------------------------------------------------------------