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Experiment 2: stoichiometry: laws to moles to molarity

Objective

  • To determine the mass of a product of a chemical reaction
  • To make a solution of assigned molarity–your accuracy will be tested by your TA by titration!

Grading

  • Pre-lab (10%)
  • Lab Report (80%)
  • TA points (10%)

Before coming to lab..

  • Read the lab instructions
  • Complete the pre-lab, due at the beginning of the lab

Introduction

The word stoichiometry derives from two Greek words: stoicheion (meaning "element") and metron (meaning "measure"). Stoichiometry deals with calculations about the masses (sometimes volumes) of reactants and products involved in a chemical reaction. Consequently, it is a very mathematical part of chemistry.

In the first part of this lab, sodium bicarbonate is reacted with an excess of hydrochloric acid.

NaHCO 3 ( s ) + HCl ( aq ) NaCl ( aq ) + CO 2 ( g ) + H 2 O size 12{"NaHCO" rSub { size 8{3} } \( s \) +"HCl" \( "aq" \) rightarrow "NaCl" \( "aq" \) +"CO" rSub { size 8{2} } \( g \) +H rSub { size 8{2} } O} {}

By measuring the mass of NaHCO 3 size 12{"NaHCO" rSub { size 8{3} } } {} and balancing the equation (above), the mass of NaCl expected to be produced can be calculated and then checked experimentally. Then, the actual amount of NaCl produced can be compared to the predicted amount.

This process includes molar ratios, molar masses, balancing and interpreting equations, and conversions between grams and moles and can be summarized as follows:

  • Check that the chemical equation is correctly balanced.
  • Using the molar mass of the given substance, convert the mass given in the problem to moles.
  • Construct a molar proportion (two molar ratios set equal to each other). Use it to convert to moles of the unknown.
  • Using the molar mass of the unknown substance, convert the moles just calculated to mass.

In the second part of this lab, since a great deal of chemistry is done with solutions, a solution will be prepared of allocated molarity. Molarity, or more correctly molar concentration, is defined to be the number of moles of solute divided by the number of liters of solution:

c M = n substance V solution size 12{c rSub { size 8{M} } = { {n rSub { size 8{ bold "substance"} } } over {V rSub { size 8{ ital "solution"} } } } } {}

with units of [mole/L]. However molar concentration depends on the temperature so a higher temperature would result in an increased volume with a consequential decrease in molar concentration. This can be a significant source of error, of the same order as the error in the volume measurements of a burette, when the temperature increases more than 5ºC.

Steps to preparing a solution of a certain concentration:

  • First need to know the formula for the solute, e.g. potassium chromate: K 2 CrO 4 size 12{K rSub { size 8{2} } "CrO" rSub { size 8{4} } } {} .
  • Need the molecular weight of the solute: by adding up the atomic weights of potassium, chromium and oxygen: 39.10, 52.00 and 16.00 in the correct ratios:
  • 2 × 39 . 1, 52 . 0 and 4 × 16 . 00 = 194 . 2g/mole . size 12{"2 " times " 39" "." "1, 52" "." "0 and 4 " times " 16" "." "00 = 194" "." "2g/mole" "." } {}
  • Then the volume of solution, usually deionised water: e.g. for one liter of solution use a 1000 mL volumetric flask. So a 1M solution would require 194.2g of solid K 2 CrO 4 size 12{K rSub { size 8{2} } "CrO" rSub { size 8{4} } } {} in 1 L, 0.1M 19.42g of solid K 2 CrO 4 size 12{K rSub { size 8{2} } "CrO" rSub { size 8{4} } } {} and so on.
  • Remember to ensure that all the solute is dissolved before finally filling to the mark on the volumetric flask. If there is any undissolved solute present in the solution, the water level will go down slightly below the mark, since the volume occupied by the solute differs from the actual volume it contributes to the solution once it is dissolved.

Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
in a comparison of the stages of meiosis to the stage of mitosis, which stages are unique to meiosis and which stages have the same event in botg meiosis and mitosis
Leah Reply
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Source:  OpenStax, Honors chemistry lab fall. OpenStax CNX. Nov 15, 2007 Download for free at http://cnx.org/content/col10456/1.16
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