S C F H C S M

S C F H C S M S

Second Midterm Exam, Fall

Your name: Your teaching fellow: Your section time:

Please write your name at the top of every page. True/false and multiple choice questions require no explanation. Show your work for all other question types. e equation sheet (the last page) may be removed for your reference.

Question ( points)

Question (points)

Question ( points)

Question (points)

Total ( points) SPU Midterm Your Name:

Problem : Multiple Choice and Short Answer Questions (points)

. (points) True or false: e viscosity of . (points) True or false: In an emulsion, chocolate sauce increases as temperature the phase which occupies the largest vol- increases. ume is always the continuous phase.

(a) True (a) True (b) False (b) False . (points) True or false: Adding cream of . (points) True or false: e elastic mod- tartar to egg whites before beating helps to ulus of an emulsion can be increased by stabilize the foam. making the droplets larger. (a) True (b) False (a) True (b) False . e reaction by which yeast ferment sugar is given below: . (points) True or false: e solubility of CHO CHCHOH CO carbon dioxide gas in water decreases as temperature increases. (a) (points)→ Fill in the blanks+ above to correctly balance the fermentation (a) True reaction. (b) False (b) (points) Name the two products of fermentation.

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Problem : anksgivukkah (points) e Jewish holiday of Hanukkah happens to fall on anksgiving this year! In order to cel- ebrate, Michelle decides to swap out her traditional dinner rolls with a lovely braided challah, a traditional egg bread.

Challah . In a large bowl, sprinkle yeast over barely warm water. From Allrecipes.com - makes loaves . Beat in sugar, oil, eggs, and salt. ⁄ cups warm water ( F/ C) . Add our one cup at a time. tbsp. active dry yeast ○ ○ . Knead until smooth and elastic and no longer sticky, adding ⁄ cup sugar our if needed. tbsp. vegetable oil eggs . Cover with a damp cloth and let rise for ⁄ hours in a warm tbsp. salt place. cups all-purpose our . Punch down the risen dough, divide in half, and knead for tbsp. poppy seeds (optional) minutes. Divide each half into thirds, roll into cylinders, and braid. ≈ . Grease two baking trays and place nished braid or round on each. Cover with towel and let rise hour. . Preheat oven to F( C). . Beat the remaining○ egg and○ brush a generous amount over each braid. Sprinkle with poppy seeds if desired. . Bake at F( C) for about minutes. When done, the bread will sound hollow when tapped on the bottom. ○ ○

. (points) How does kneading the dough aect the bread’s elasticity? (Circle one.)

. Increases elasticity No eect Decreases elasticity .

. (points) Why does the dough rise during steps and ? Explain in -sentences.

. (points) Michelle decides to use a chemical leavener in place of yeast to save time. Should she use baking powder or baking soda? Why?

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Michelle will have lots of family in town this year, so she buys a frozen -pound turkey instead of the usual -pound turkey. Approximate the turkeys as solid spheres of the same (uniform) density.

. (points) Approximately how much longer than usual will it take to cook the turkey this year? Express your answer as a fold change.

. (points) Describe two steps Michelle can take to minimize the cooking time of the turkey.

Problem : Egg Custard ( points) You feel pretty bad about what you did to Mike’s tofu during the rst midterm. To make it up to him, you bake him egg custard, his favorite dessert. You nd the following recipe on a reputable egg custard appreciation site, eggcustardfanciers.com:

Egg Custard . Place a saucepan on medium heat and add mL of milk. . Add vanilla extract as the milk simmers. mL milk . In a separate bowl, whisk egg yolks and sugar. tsp. vanilla extract . Whisk our into egg yolk mixture until paste forms. egg yolks . Pour half of warmed milk into egg yolk mixture, whisking tsp. ( g) our until the consistency is uniform throughout. ⁄ cup ( mL) sugar . Add egg yolk mixture back into remaining milk on medium heat, stirring occasionally, for three minutes. enal egg custard is supposed to be much more viscous than if the ingredients had been simply mixed together.

. (points) Give two reasons why the mixture becomes more viscous on heating.

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Amylose is a polysaccharide found in our made up of glucose monomers. Each monomer has a radius of roughly .nm and weighs amu. ≈ . (points) What is the eective radius≈ of each amylose molecule, assuming it behaves as a random coil when dissolved in water?

. (points) What is the eective volume occupied by each amylose molecule?

. (points) What is the molecular weight of amylose (in g/mol)?

. (points) Amylose makes up approximately % of our by weight. How many molecules of amylose are present?

. (points) What is the total volume occupied by amylose molecules in this recipe? Express your answer in liters.

. (points) If the combined volume of the ingredients is mL, what is the volume fraction of the amylose?

. (points) Does amylose alone make the custard signicantly more viscous? Explain in one sentence.

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. (points) e mix is far too runny at the end of the procedure. Describe a backup method for making the custard more viscous.

Problem : Guacamole ( points) Guacamole is delicious. However, you know from experience that if you leave it uncovered on a countertop for too long, it will change color and become brown.

. (points) Why does guacamole turn brown? What are the molecules involved?

. (points) For each of the following, please describe how each of the following would aect the rate of browning in guacamole by circling the appropriate response.

(a) Decreasing the temperature from Cto C. ○ ○ . Decreases browning rate No eect Increases browning rate .

(b) Increasing the temperature from Cto C. ○ ○ . Decreases browning rate No eect Increases browning rate .

(d) Storing the guacamole under oil. . Decreases browning rate No eect Increases browning rate .

(e) Adding extra lime juice to the guacamole. . Decreases browning rate No eect Increases browning rate .

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Problem : Baked Alaska (points)

Baked Alaska is made by placing ice cream on top of a layer of pre-cooked cake, then enclosing the whole business in a cm-thick layer of meringue (whipped egg whites and table sugar). eBaked Alaska is then heated in an oven until the meringue begins to rm up, ideally with minimal ice cream melting.

Aer being beaten, the egg white and sugar take up four times their original volume.

. (points) What is the volume fraction of air in the meringue?

. (points) Would you expect the meringue to behave as a solid (e.g., hold stipeaks) before being cooked? Explain why or why not in -sentences.

. (points) If the Baked Alaska is cooked at C, two types of browning will occur. Fill in the blanks below to describe each browning process.○

Name of process:

Minimum temperature required:

Molecule type(s) required:

Meringue ingredient(s) providing the molecule(s) required:

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. (points) Approximately how long would it take for heat to just barely pass through the cm-thick meringue layer and reach the ice cream? Assume for simplicity that the diusion coecient of heat through meringue is approximately the same as that of heat through water. Give your answer in minutes.

Joey bakes his Baked Alaska for een minutes at an oven temperature of C. Before baking, the entire dessert was at - C (the○ temperature inside his freezer). ○

. (points) Sketch (with a solid line) the temperature distribution when the Baked Alaska is removed from the oven. Indicate on the y- axis the approximate temperature at which ice cream melts.

When the nished Baked Alaska is transferred to a serving dish, melted ice cream begins to pool at the base! In a Hail-Mary eort to salvage the Baked Alaska, Joey throws it in the freezer for min.

. (points) On the same axes as above, sketch (with a dotted line) the nal temperature distribution inside the Baked Alaska aer it has cooled ve minutes in the freezer.

Joey uses dish soap and running water to clean up the pots and pans at the end of the day. e soap molecules are amphiphilic.

. (points) Why is it easier to clean the dishes with soap than with water alone? Explain in - sentences.

SPU Midterm Your Name:

Conversions and short formulas Pa = N/m N=kg m/s J=Nm L=x m =J/m − ⋅ Kelvin⋅ = Fahrenheit = Surface area of a mL = cm Celsius + (Celsius ⁄)+ sphere = πr Laplace pressure Volume of a sphere = Polymer radius σ ⋅ ∆p r ⁄πr rp rm Nm Constants √ = = Gravitational Avogadro’s number Cal=cal Room temp = C acceleration . x =. kJ ○ g= m/s molecules/mol

Boltzmann constant Specic heat of water Dheat in water DCa in water kB =.x J/K . J/g K .x cm /s .x+ m /s − Prexes − − ⋅ giga (G): mega (M): kilo (k): centi (c): milli (m): micro (µ): nano (n): A=˚ m− − − − −

Equation Description Units Concentration of hydrogen pH log H H mol/L + + ions = − [ ][Q ] Heat J Q mc ∆T m Mass g p cp Specic heat capacity J/g K or J/g C ∆T Change in temperature K or C ⋅ ⋅ = Uint Interaction energy J ○ U ck T c Constant – int B kB Boltzmann constant J/K T Phase transition temperature T = E Elastic modulus Pa F A F Force N Area over which force is E A m ∆L L applied = ∆L Change in length m L Initial length m E Elastic modulus Pa Uint E Uint Interaction energy J Crosslink distance m L Distance of diusion m L = Dt D Diusion coecient m/s √ t Time to diuse s = SPU Midterm Your Name:

Equation Description Units Volume fraction of Unitless dispersed phase Vdispersed V Volume of dispersed total V L dispersed phase = Vtotal Total Volume L E Elastic Modulus Pa σ Surface tension N/m σ E R c R Droplet radius m Dispersed phase Unitless volume fraction = ( − ) Critical volume c fraction (.) Unitless Sodium bicarbonate NaHCO mol (baking soda)

CHCOOH Acetic acid mol NaHCO + CHCOOH .... NaCHO +HO+CO NaC H O Sodium acetate mol →

HO Water mol

CO Carbon dioxide gas mol k Reaction rate s − k Max. reaction rate ∼ s ∆u kBT − k ke ∆u Activation energy∼ J − k Boltzmann constant J/K = B T Temperature K Number of microbes at N t Microbes time t kt N t Ne ( ) Initial number of N Microbes t τ microbes N ( ) = k Rate of growth/death s ln − where k = τ t Time elapsed s = τ Doubling time s