Lab 2: Melting Points

In this lab, you will be using a _____________ apparatus to measure melting point ranges

Mel-temp

Because the presence of impurities affects the melting point of a compound, the melting point can be a good indicator of __________

Purity

Melting points are always measured as a _______

Range

Although you will only have 1 unknown to identify in the lab, how many compounds are possible options for the unknown in this experiment?

12

While directly measuring a melting point in the lab, you should use a setting on the apparatus so that the temperature rises no more than __ to __ degrees per minute

2 3

To perform a melting point determination, a small amount of powdered sample is placed inside a melting point __________________

Capillary tube

Impure samples have melting point ranges that are both _____________ and _____________ compared to a pure sample

Depressed Broadened

The phenomenon of melting point depression is used in every-day life during the winter whenever roads are salted. Ice and salt are mixed together to lower the melting point of water, making roads less slippery until colder temperatures. The precise composition of salt and ice to yield the lowest melting point temperature is with 23 wt% salt. This value is called the ___________ point for a mixture

Eutectic

You have an unknown compound that has a melting point range of 162-164 °C. You know that the unknown is either salicylic acid (MP range: 158-160 ºC), l-arabinose (MP range: 160-163 °C), triphenylcarbinol (MP range: 160-163 °C), benzanilide (MP range: 162-164 °C), or sulfanilamide (MP range: 165-167 °C). You create mixtures of the unknown with each of the five possible compounds and obtain the following data: Unknown + salicylic acid-- MP range: 161-163 °C Unknown + l-arabinose-- MP range: 154-160 °C Unknown + triphenylcarbinol-- MP range: 150-163 °C Unknown + benzanilide-- MP range: 157-164 °C Unknown + sulfanilamide-- MP range: 155-163 °C Based on this data, what is the identity of the unknown most likely to be? a. salicylic acid b. l-arabinose c. triphenylcarbinol d. benzanilide e. sulfanilamide

a. salicylic acid

If you mix compound A (melting point range: 43-44 °C) with compound B (melting point range: 44-45 °C), then you will observe the mixture to have a melting point range of 43-45 °C a. true b. false

b. false

In the lab, melting points are measured as single temperature values a. true b. false

b. false

The melting point of a compound is the temperature at which it begins to transition from solid to liquid a. true b. false

b. false

Crushing a solid compound into a fine powder results in a _____ melting point range than melting one large crystal a. less accurate b. more accurate c. lower d. higher

b. more accurate

Maleic acid and malonic acid have very similar names, and coincidentally, very similar melting point ranges. Maleic acid melts between 134-136 °C, and malonic acid melts between 135-137 °C. If a student inadvertently returned some malonic acid to the maleic acid jar, which of the following melting point ranges would you expect to find of the maleic acid mixture now? a. 134-136 °C b. 135-137 °C c. 130-135 °C d. 136-140 °C

c. 130-135 °C

Based on the Mel-Temp heating curve below, what is the best setting to use to measure the melting point range of a compound with a literature melting point range of 77-78 °C? a. 5 b. 4 c. 3 d. 2

c. 3

Based on the Mel-Temp heating curve below, what is the best setting to use to measure the melting point range of a compound with a literature melting point range of 202-203 °C? a. 8 b. 7 c. 6 d. 5

c. 6

The faster one performs a melting point determination, the _____ the melting point range will be a. faster b. slower c. less accurate d. more accurate

c. less accurate

You have an unknown compound that has a melting point range of 162-164 °C. You know that the unknown is either salicylic acid (MP range: 158-160 ºC), l-arabinose (MP range: 160-163 °C), triphenylcarbinol (MP range: 160-163 °C), benzanilide (MP range: 162-164 °C), or sulfanilamide (MP range: 165-167 °C). You create mixtures of the unknown with each of the five possible compounds and obtain the following data: Unknown + salicylic acid-- MP range: 151-163 °C Unknown + l-arabinose-- MP range: 154-160 °C Unknown + triphenylcarbinol-- MP range: 160-163 °C Unknown + benzanilide-- MP range: 155-162 °C Unknown + sulfanilamide-- MP range: 150-164 °C Based on this data, what is the identity of the unknown most likely to be? a. salicylic acid b. l-arabinose c. triphenylcarbinol d. benzanilide e. sulfanilamide

c. triphenylcarbinol

Based on the two groups of compounds being used in this experiment, which of the following compounds does not belong within the same melting point group as the others? a. maleic acid b. urea c. trans-cinnamic acid d. benzoin e. benzanilide f. benzamide

e. benzanilide