Homework Help

[STLRamsFan]

Having a little brain fart and completely forgot how to do this :|

"A thermometer containing 4.2 grams of mercury has broken. If mercury has a density of 13.6 g/mL, what volume spilled?"





57 mL




3.2 mL




0.3088 mL




0.31 mL



(Weird formatting, those were the choices I was given)

[Skyline]

Been too long, http://www.wolframalpha.com/input/?i=4.2+g+of+mercury+to+mL

[TPBlinD]

4.2 grams by 13.6g/ml would be 4.2 * 13.6 which equals 666

[CN3089]

Having a little brain fart and completely forgot how to do this :|

"A thermometer containing 4.2 grams of mercury has broken. If mercury has a density of 13.6 g/mL, what volume spilled?"





57 mL




3.2 mL




0.3088 mL




0.31 mL



(Weird formatting, those were the choices I was given)

4.2*(13.6^-1) = .3088 which you should round to .31, since something something significant digits.

[STLRamsFan]

Thanks guys, here's two other ones I just want to be sure. Still getting used to the whole sig figures again:

74.32 cm + 165.90 cm + 0.036 cm






240.26 cm




240.256 cm




240.2 cm




240.25 cm

I chose the first one



For the following problem, choose the answer with the correct number of significant figures: 1.55 / (2) (46)

Answer



0.01




0.0168




1.7 x 10-3




0.02

I chose the last one.

[sleepy1212]

I can't remember if .90 counts as two sig figs, last one is right.

[Timo]

.90 counts as two, which brings the total number of significant figures to five in that number so it doesn't really matter.

[Patrickssj6]

4.2 grams by 13.6g/ml would be 4.2 * 13.6 which equals 666
You can check you calculation in 2 ways:

1. 4.2g * 13.6 g/ml would be 666 g/ml*g so that cannot be right since they just want ml.
2. 4.2 grams result in half a liter? :P

[n00b1n8R]

Not a direct answer but one of the most useful skills to develop when you're doing any dimension based computation is dimensional analysis. If you know what numbers you need and you know their units and the units of the answer you're trying to get, just look at them and see what needs to be multiplied/divided. It gets me out of a lot of trouble when I forget that one fucking formula on exams :P

You started with N mass and Y mass/volume and wanted your answer in volume.

so you just go mass*(mass/volume)^-1 and let the units cancel to give volume.

[Limited]

Rams, isnt the answer to the first one just = 4.2 / 13.6? Or am I just an idiot here...

Also 'Homework'? Damn I feel old.

[CN3089]

Rams, isnt the answer to the first one just = 4.2 / 13.6? Or am I just an idiot here...

Also 'Homework'? Damn I feel old.

yes, g/(g/mL) = mL. It's more a test of knowing what to round it to, high school chemistry uses the significant digits thing.

[sleepy1212]

so does college chemistry/physics/science

[Phopojijo]

Having a little brain fart and completely forgot how to do this :|

"A thermometer containing 4.2 grams of mercury has broken. If mercury has a density of 13.6 g/mL, what volume spilled?"






57 mL




3.2 mL




0.3088 mL




0.31 mL




(Weird formatting, those were the choices I was given)When solving these questions -- remember what you are trying to accomplish.

4.2g of Mercury... ... Mercury has a density of 13.6 g/ml.

http://img.photobucket.com/albums/v342/Phopojijo/unitconversion.png

[Donut]

yeah just to add to that^ btw, 13.6 g/ml -> 0.07352941176 ml/g. remember if you reciprocate the unit, you need to reciprocate the number too (do 1/number, or (number)^-1)

dumbE: or dont fucking listen to me and just divide by 13.6. its the same thing i said, but with less stupid decimals. and frankly, im pretty sure all those decimals are completely counter-productive to the significant figure thing. but you know for future reference now at least.

[STLRamsFan]

Thanks for the help with the last assignment guys, sure helped me out on the next several things...

This one I'm really have a brain fart on:

"Several different elements were identified using the flame tests. Which of these elements would be a good choice for a fireworks display? Why?"

Flame Tests

Soultion Metal Ion Color

NaC1 +1 Na Orange
KC1 +1 K Pink/Light Red
BaC12 +2 Ba light green/yellow
CaC12 +2 Ca Red/Dark Orange
SrC12 +2 Sr Red
CuC12 +2 Cu Green

[n00b1n8R]

Just so we're clear, you're talking about carbides right? (NaC) and not NaCl (the one's on the end are making me think you're misreading the question)

[STLRamsFan]

Yea I'm pretty sure I am, the letters and numbers (NaC1, BaC1, ect) were the solutions we were given on the table, the metal ion and color we had to figure out on our own. Never talked about it once in lab or lecture and we're expected to do an assignment on it... Wonderful.

[sleepy1212]

You're thinking about this too hard. This is one of those questions you answer based on procedure. In other words, which of those burned easily and brightly?

[STLRamsFan]

Slamming my head into the wall on this one... 3(x+4)^2=21 (Solve the equation by the square root property)

Completely forgot how to solve this one. Been solving the others just fine but I'm stuck with the what to do with the 3 outside of the () and the 2 squared.

[Donut]

order of operations and parentheses mean that (x+4) is one term. so you have 3(x+4)2 = 21.

first thing you want to do is isolate the (x+4)2, so divide both sides by 3, which gives (x+4)2 =7

now we get rid of that square by taking the square root of both sides, which gives x+4 = ±sqrt(7). remember that because we took the square root of 7, the resulting number (which we will leave as sqrt(7) for simplicity) could be positive OR negative (because, for example, 3*3 = 9, and (-3)*(-3) also = 9)

so finally, subtract 4 from both sides. x = ±sqrt(7) - 4

please tell me i didnt fuck that up. i would feel so bad if i did

[STLRamsFan]

That makes perfect sense, thanks. For whatever reason the book didn't explain this particular problem and I completely forgot how to do it.

[n00b1n8R]

Rams, what are you studying?

[TheGhost]

Thanks guys, here's two other ones I just want to be sure. Still getting used to the whole sig figures again:

74.32 cm + 165.90 cm + 0.036 cm

240.26 cm
240.256 cm
240.2 cm
240.25 cm


I chose the first one


None of those is correct. The correct answer is 240

[Donut]

why wouldnt it be 4? i never got this significant figure thing down, but from what i saw in my physics work, the number with the least amount of precision sets how many significant figures to use.

[Timo]

The third number only has two significant figures, so the correct answer would be 240. Maybe the question was about decimal places instead?

[CN3089]

None of those is correct. The correct answer is 240

addition/subtraction works differently.

[Phopojijo]

No Ghost, it's #1.

Think of it this way... if you can measure something down to the hundredth of a millimeter... you will know that it's 0 millimeters, 0 centimeters, 0 decimeters... ... ... so they're kind-of implied significance.

That does NOT hold true for multiplication, however, where leading and trailing 0's don't affect the answer *at all* and thus cannot increase the precision of your answer.

[STLRamsFan]

Rams, what are you studying?

I'm studying Health Sciences with a concentration (at the moment) in Health Promotion and Wellness. Could possibly change that to a concentration in Senior Fitness but we'll see how it goes since I'm not officially in the division I need to be in, hopefully I'll get in it after this semester but we'll see how that goes. Kinda annoyed at the fact I need to take another math since I thought all my maths transferred but apparently only one didn't transfer which is forcing me to take algebra. Always a joy (sike)

[STLRamsFan]

Seriously cannot find this anywhere in the book nor online.... I get the use of prefixes but what the heck is the answer to this?



Prefixes are necessary with covalent compounds because:

Answer



A: two nonmetals can form more than one compound




B: two metals can form more than one compound




C: nonmetals can have positive and negative ionic charges




D: two nonmetals can form only one compound



I answered A since I ran out of time to submit it. Least I got all the other questions right. Was I right with it or no?

[sleepy1212]

A is correct.

CH2, CH3, CH4, H2O, H2O2, etc...

[STLRamsFan]

Just found that out. Thanks. Knew it had to do with nonmetals but just wasn't 100% about the other half of the answer.

Anyway, I already answered these practice exam questions and I'm pretty sure I got these right. However, I just want to be sure since I'm struggling on the quizzes but am doing fine on the exams and want to continue that. Much appreciated... Y'all have been really helpful for me in this class:

(Sorry for the bad formatting, the worksheets are a bit of a pain to format here)


When the reaction of aluminum and chlorine to form aluminum chloride is written as a properly balanced equation, the coefficient of aluminum is:

Answer



3




6




1




2






The reaction of hydrogen and oxygen to form water is best described as which type of reaction?

Answer



combination




double replacement




decomposition




single replacement







In the reaction Al + FeCl3 → Fe + AlCl3 which substance is oxidized?

Answer



Fe+3




Al




Al+3




Fe







One of the correctly balanced product terms for the double replacement reaction of iron (II) chloride and sodium sulfide is:

Answer



Na2Cl2




3NaCl




FeS




2FeSO4





Which of the following can be changed when balancing an equation?

Answer



superscript




exponent




subscript




coefficient





When iron combines with oxygen to form iron (III) oxide, which substance is reduced?

Answer



iron (III) oxide




iron (II) oxide




iron




oxygen





When calcium carbonate is heated it produces calcium oxide and carbon dioxide gas. What type of reaction is this?

Answer



decomposition




single replacement




combustion




double replacement






How many atoms of hydrogen are found on the product side of the correctly balanced equation in the reaction of aluminum sulfate with potassium hydroxide?

Answer



5




2




6




3





Which of the following is an example of a physical change?

Answer



burning a match




water freezing into an icicle




tarnishing of a silver bracelet




digesting a chocolate bar





When a carbon compound reacts with oxygen to form carbon dioxide, water and energy what type of reaction takes place?

Answer



combustion




single replacement




decomposition




double replacement