1. How many kilos of potatoes would you like?

2. I went fishing but I didn't catch any fish.

3. Cook the chicken over low heat for 15 minutes before you serve it.

4. Can you tell me how to cook broken rice?

5. There are three cartons of milk in the fridge.

6. He has an egg but he hasn't got any bread.

7. Pho is one of the most popular dishes in Vietnam.

1) \(\left(\dfrac{-13}{17}-\dfrac{31}{52}\right)-\left(\dfrac{73}{52}-\dfrac{13}{17}+\dfrac{5}{6}\right)-\dfrac{3}{4}\)

\(=\dfrac{-13}{17}-\dfrac{31}{52}-\dfrac{73}{52}+\dfrac{13}{17}-\dfrac{5}{6}-\dfrac{3}{4}\)

\(=\left(\dfrac{-13}{17}+\dfrac{13}{17}\right)-\left(\dfrac{31}{52}+\dfrac{73}{52}\right)-\left(\dfrac{5}{6}+\dfrac{3}{4}\right)\)

\(=0-2-\dfrac{19}{12}\)

\(=-2-\dfrac{19}{12}\)

\(=\dfrac{-43}{12}\)

2) \(\dfrac{1}{7}.\dfrac{1}{3}+\dfrac{1}{7}.\dfrac{1}{2}-\dfrac{1}{7}\)

\(=\dfrac{1}{7}\left(\dfrac{1}{3}+\dfrac{1}{2}-1\right)\)

\(=\dfrac{1}{7}.-\dfrac{1}{6}\)

\(=-\dfrac{1}{42}\)

3) \(\dfrac{13}{123}.\dfrac{1}{2}-\dfrac{1}{3}.\dfrac{13}{123}+\dfrac{1}{6}.\dfrac{110}{123}\)

\(=\dfrac{13}{123}.\left(\dfrac{1}{2}-\dfrac{1}{3}\right)+\dfrac{1}{6}.\dfrac{110}{123}\)

\(=\dfrac{13}{123}.\dfrac{1}{6}+\dfrac{1}{6}.\dfrac{110}{123}\)

\(=\dfrac{1}{6}\left(\dfrac{13}{123}+\dfrac{110}{123}\right)\)

\(=\dfrac{1}{6}.\dfrac{123}{123}\)

\(=\dfrac{1}{6}\)

PTHH: Al2O3+6HCl➝2AlCl3+3H2O(1)

a)nAl2O3=\(\dfrac{10,2}{102}\)=0,1(mol)

   mHCl=\(\dfrac{5\%.219}{100\%}\)=10,95(g)

   ⇒nHCl=\(\dfrac{10,95}{36,5}\)=0,3(mol)

Xét tỉ lệ Al2O3:\(\dfrac{0,1}{1}\)=0,1

Xét tỉ lệ HCl:\(\dfrac{0,3}{6}\)=0,05

⇒HCl pứng hết,Al2O3 còn dư

Theo PTHH(1) ta có nAl2O3 pứng=\(\dfrac{nHCl}{6}\)=\(\dfrac{0,3}{6}\)=0,05(mol)

⇒nAl2O3 dư=nAl2O3ban đầu-nAl2O3 pứng=0,1-0,05=0,05(mol)

⇒mAl2O3 dư=0,05.102=5,1(g)

b) C%HCl=\(\dfrac{0,3.36,5}{219+10,2}\).100%=4,8%

     nAlCl3=0,1(mol)

⇒C%AlCl3=\(\dfrac{0,1.136,5}{10,2+219}\).100%=6%