Chem 100L: Exam 3

What are food additives?

chemcials added to food to improve preservation, Nutrition, flavor, or appearence

Who regulates food dyes in the U.S.?

the FDA regulates all food dyes used in foods, drugs and cosmetics

What is the difference between natural and synthetic dyes?

• Natural dyes: come from sources like plants ( turmeric, carotenoids, chlorophyll)

• Synthetic dyes: manmade, cheaper, and have Longer shelf life

Do powdered drink mixes contain food dyes?

to influences perceived flavors by matching color with expected taste

What does a spectrophotometer measure?

the amount of light absorbed or transmitted by a solution

What is absorbance (A)?

the amount of light absorbed by a sample; Unitless

What is % transmittance (%T)?

the percentage of light that passes through a sample

What is λmax?

the wavelength where maximum absorbance occurs

Why is λmax important?

• gives the most accurate absorbance that occurs

• required for beer’s law calculations

What are the visible light wavelength ranges?

400-700 nm

What is Beer’s law?

• The amount of absorbed light is directly proportional to the solution concentration

• A = ε c l

What is ε?

the molar extinction coefficients

What variables are plotted in a Beer-law’s plot?

• Absorbances (y-axis)

• Concentration (x-axis)

What is the expected shape of a Beer’s law plot?

a straight line showing direct proportion

What is the formula used for dilutions?

C1V1=C2V2

how to convert mM to M

divide by 1000

how do you determine concentration from a line equation

Solve X=(y-b)/m

What does a 10x dilution mean?

the orignals concentration is 10X higher then the diulted sample

how do you calculate mass od dye from the concentration?

• convert M x L to moles

• mulitply moles x moles mass

How do you calculate mass percent?

(Mass of dyes ÷ mass of powder) x 100

What is an acid?

• a substance that produce H+ ions in water

• sour taste

What is a base?

• a substance that produce OH- in solution

• feels slippery or soapy, bitter taste

What is titration?

An analytical technique used to find an unknown concentration using a known solution

what is the titrants?

the solution in the burette with known concentration

What is the analyte?

the solution in the flask with unknown concentration

What is the neutralization reaction for HCI and NaOH?

HCl + NaOH → NaCl + H2O.

What is the equivalence point?

when moles of acid = moles of base

What indicator is used in this lab?

Phenolphthalein

What color changes show the endpoint?

colorless to faint pink

At what pH range does phenolphalein change color?

pH 8.2-10

How do you read a burette?

to the nearest 0.01mL

How do you calculate volume dispensed?

final reading—initial reading

what is the simplified titration formula

M acid V acid = M base V base

How do you find moles from molarity?

Moles=M x V (in liter)

What are the reactants in aspirin synthesis?

1. salicylic acid

2. acetic anhydride

what is the product

aspirin (acetylsalicylic acid)

What is the catalyst?

sulfuric acid

What triggers crystallization?

adding water after heating the reaction mixture

Why is an ice bath used?

to help aspirin crystals form

What is the limiting reactant?

The reactant consumed first determines theoretical yeildyield.

How do you calculate percent yield?

(actual yield ÷ theoretical yield) x 100

What does the ferric chloride test detect?

phenolic -OH group

What color means salicylic acid is present?

purple

What color indicates pure aspirin?

yellow (negatives test)