When youre done M ake sure to make your DAY 2 observations for the Egg tastic Class Inquiry httpswwwyoutubecomwatchvkxPwbhFeZSw 43 Homework Questions 4 What is the pH of an aqueous solution containing 000200 M barium hydroxide ID: 488712
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Slide1
Pre-Lab Quiz
When you’re done:
M
ake sure to make your
DAY 2 observations
for the
Egg-
tastic
Class Inquiry Slide2
https://www.youtube.com/watch?v=kxPwbhFeZSwSlide3
4.3
Homework Questions
4. What is the pH of an aqueous solution containing 0.00200 M barium hydroxide,
Ba
(OH)
2
7. A 2.67g sample of hydrogen fluoride gas (HF) is dissolved in sufficient water to make 1.05L of solution at 25C to form an acidic solution. Hydrogen fluoride is a weak acid with Ka= 6.6x10
-4
Calculate the pH of the solution
Calculate the
pOH
of the solution Slide4
Indicators, Neutralizations & Titrations RevisitedSlide5
Indicators
Indicators are dyes that
change
colour
under varying conditions of acidity.
Although not as accurate as instruments such as pH meters in determining acidity, indicators can be used to give
less precise measure of acidity
.
Litmus
is a very commonly used indicator which is red in acids and blue in bases. Litmus is an indictor that changes colour from red to blue in the pH range of 5.5 to 8.0. Slide6
Indicators
Indicators are
coloured
compounds that exist in both acidic and basic forms.
A general formula may be used for indictors -
HIn
- and a reaction written:
HIn
↔ H
+
+ In- acidic form basic form colour 1 colour 2
Indicators may be in solution form or paper form. pH paper is prepared by treating the paper with the indictor solution. When the paper is then dipped into the solution you are testing, it will change colour depending on the acidity of the solution.Slide7
Find my pH Activity
Indicator used: Purple cabbage
Purple cabbage contains colored pigments (one of which is
anthocyanin
) that change colors when they meet an acid or a base. Acids make purple cabbage juice turn pink. Bases make the juice turn blue or greenish.Slide8
Indicator Examples
Indicator
pH range
Colour
change
methyl orange
3.2 - 4.4
red to yellow
litmus
5.8 - 8.0
red to blue
phenolphthalein8.2 - 10.0colourless to pink1. A given solution turns methyl orange yellow, litmus blue, and phenolphthalein pink. What is the approximate pH of the solution?Methyl orange in yellow when pH is above 4.4Litmus is blue when pH is above 8.0, andPhenolphthalein is red when pH is above 10.0. Therefore the solution would have to have a pH above 10.0Slide9
Indicator Examples
Indicator
pH range
Colour
change
methyl orange
3.2 - 4.4
red to yellow
litmus
5.8 - 8.0
red to blue
phenolphthalein8.2 - 10.0colourless to pink2. What color would methyl orange, litmus, and phenolphthalein turn when testing:a. vinegar (pH = 3)Methyl orange: redLitmus: redPhenolphthalein: colorlessb. sea water (pH = 8)Methyl orange: yellowLitmus: bluePhenolphthalein: colorlessSlide10
Neutralization Reactions
What happens when an acid such as
HCl
is mixed with a base such as
NaOH
:
HCl
(
aq
)
+ NaOH(aq) → NaCl(aq) + H2
O(l)When an acid and a base are combined, water and a salt are the products.Salts are ionic compounds containing a positive ion other than H+ and a negative ion other than the hydroxide ion, OH-.Double displacement reactions of this type are called neutralization reactions.We can write an expanded version of this equation, with aqueous substances written in their longer form:H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) → Na+(aq) + Cl-(aq) + H2O(l)Removing the spectator ions we get the net ionic equation:H+(aq) + OH-(aq) → H2O(l)Slide11
Titrations
A titration is a laboratory procedure used to determine the
concentration
of a solution.
During an acid-base titration an acid with a known concentration (standard solution) is added to a base with an unknown concentration (or vice-versa).
An indicator is also added to the solution which will signal (by a color change) when the base has been
neutralized
.Slide12
Titrations
Note that as soon as you see a color change the titration is complete and the
[H
+
] and [OH
-
]
are equal.
At this
equivalency point
the titration is stopped. By knowing: the initial volume of the base, the volume of acid added, and the initial concentration of the acid we can calculate the concentration of the base.Slide13
Titration Examples
During a titration 75.8
mL
of a 0.100 M standard solution of
HCl
is titrated to end point with 100.0
mL
of a
NaOH
solution with an unknown concentration. What is the concentration of the
NaOH solution?Slide14
2)
A
20.0
mL
solution of strontium hydroxide,
Sr
(OH)
2,
is placed in a flask and a drop of indicator is added. The solution turns colour after 25.0
mL
of a standard 0.0500 M HCl solution is added. What was the original concentration of the Sr(OH)2 solution?